View source for Body mass index

{{pp-vandalism|small=yes}}
{{pp-pc1}}
{{short description|Measure of relative weight based on an individual's mass and height}}
{{Use British English Oxford spelling|date=September 2016}}
{{Infobox diagnostic
| name = Body mass index (BMI)
| synonyms = Quetelet index
| image = BMI chart.svg
| alt = 
| caption = A graph of body mass index as a function of body mass and body height. The dashed lines represent subdivisions within a major class.
| pronounce = 
| DiseasesDB = <!--{{DiseasesDB2|numeric_id}}-->
| ICD10 = <!--{{ICD10|Group|Major|minor|LinkGroup|LinkMajor}} or {{ICD10PCS|code|char1/char2/char3/char4}}-->
| ICD9 = 
| ICDO = 
| MedlinePlus = 007196
| eMedicine = <!--article_number-->
| MeshID = D015992
| OPS301 = <!--{{OPS301|code}}-->
| LOINC = {{LOINC|39156-5}}
| HCPCSlevel2 = 
| OtherCodes = 
| reference_range = 
}}

'''Body mass index''' ('''BMI''') is a value derived from the [[mass]] ([[Mass versus weight|weight]]) and [[height]] of a person. The BMI is defined as the [[human body weight|body mass]] divided by the [[square (algebra)|square]] of the [[human height|body height]], and is universally expressed in [[Units of measurement|units]] of kg/m<sup>2</sup>, resulting from mass in [[kilogram]]s and height in [[metre]]s.

The BMI may be determined using a table<ref group=note>e.g., the [http://www.nhlbi.nih.gov/guidelines/obesity/bmi_tbl.htm Body Mass Index Table] {{webarchive|url=https://web.archive.org/web/20100310114919/http://www.nhlbi.nih.gov/guidelines/obesity/bmi_tbl.htm |date=2010-03-10 }} from the [[National Institutes of Health]]'s [[National Heart, Lung, and Blood Institute|NHLBI]].</ref> or chart which displays BMI as a function of mass and height using contour lines or colours for different BMI categories, and which may use other units of measurement (converted to metric units for the calculation).<ref group=note>For example, in the UK where people often know their weight in [[Stone (unit)|stone]] and height in feet and inches, – see {{cite web |url=http://newsimg.bbc.co.uk/media/images/42028000/gif/_42028890_bmi_gra_416x314.gif |title= |access-date=2013-07-29 |url-status=live |archive-url=https://web.archive.org/web/20121111002050/http://newsimg.bbc.co.uk/media/images/42028000/gif/_42028890_bmi_gra_416x314.gif |archive-date=2012-11-11 |df= }}</ref>

The BMI is a convenient [[rule of thumb]] used to broadly categorize a person as ''underweight'', ''normal weight'', ''overweight'', or ''obese'' based on tissue mass ([[muscle]], fat, and bone) and height. That categorization is the subject of some debate about where on the BMI scale the dividing lines between categories should be placed.<ref>{{cite web |url=https://www.independent.co.uk/life-style/health-and-families/features/why-being-overweight-means-you-live-longer-the-way-scientists-twist-the-facts-10158229.html |title=Why being 'overweight' means you live longer: The way scientists twist the facts |author=Malcolm Kendrick |publisher=[[The Independent (newspaper)|https://www.independent.co.uk]] |date=April 12, 2015 |access-date=12 April 2015 |url-status=live |archive-url=https://web.archive.org/web/20150412201212/http://www.independent.co.uk/life-style/health-and-families/features/why-being-overweight-means-you-live-longer-the-way-scientists-twist-the-facts-10158229.html |archive-date=12 April 2015 |df= }}</ref>  Commonly accepted BMI ranges are underweight: under 18.5&nbsp;kg/m<sup>2</sup>, normal weight: 18.5 to 25, overweight: 25 to 30, obese: over 30.<ref name="WHO Mean Body Mass Index BMI">{{cite web |title=WHO Mean Body Mass Index (BMI) |url=https://www.who.int/gho/ncd/risk_factors/bmi_text/en/ |publisher=World Health Organization |accessdate=5 February 2019}}</ref>

BMIs under 20.0 and over 25.0 have been associated with higher all-causes mortality, with the risk increasing with distance from the 20.0–25.0 range.<ref>{{cite journal |last1=Di Angelantonio E, Bhupathiraju ShN|display-authors=etal|title=Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents |journal=Lancet |date=2016-08-20 |volume=388(10046) |issue=776–86 |pages=776–786|pmc=4995441|pmid=27423262|doi=10.1016/S0140-6736(16)30175-1}}</ref>
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==History==
[[File:Obesity & BMI.png|thumb|Obesity and BMI]]
[[Adolphe Quetelet]], a Belgian astronomer, mathematician, statistician, and sociologist, devised the basis of the BMI between 1830 and 1850 as he developed what he called "social physics".<ref>{{cite journal | vauthors = Eknoyan G | title = Adolphe Quetelet (1796–1874)--the average man and indices of obesity | journal = Nephrology, Dialysis, Transplantation | volume = 23 | issue = 1 | pages = 47–51 | date = January 2008 | pmid = 17890752 | doi = 10.1093/ndt/gfm517 }}</ref> The modern term "body mass index" (BMI) for the ratio of [[human body weight]] to squared height was coined in a paper published in the July 1972 edition of the ''[[Journal of Chronic Diseases]]'' by [[Ancel Keys]] and others. In this paper, Keys argued that what he termed the BMI was "...if not fully satisfactory, at least as good as any other relative weight index as an indicator of relative obesity".<ref>{{cite journal | vauthors = Blackburn H, Jacobs D | title = Commentary: Origins and evolution of body mass index (BMI): continuing saga | journal = International Journal of Epidemiology | volume = 43 | issue = 3 | pages = 665–669 | date = June 2014 | pmid = 24691955 | doi = 10.1093/ije/dyu061 | url = https://academic.oup.com/ije/article-pdf/43/3/665/9728399/dyu061.pdf | doi-access = free }}</ref><ref>{{cite magazine |url= http://www.slate.com/id/2223095/ |title= Beyond BMI: Why doctors won't stop using an outdated measure for obesity |author= Jeremy Singer-Vine |magazine= [[Slate (magazine)|Slate.com]] |date= July 20, 2009 |access-date= 15 December 2013 |url-status=live |archive-url= https://web.archive.org/web/20110907125413/http://www.slate.com/id/2223095 |archive-date= 7 September 2011 }}</ref><ref>{{cite journal | vauthors = Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL | title = Indices of relative weight and obesity | journal = Journal of Chronic Diseases | volume = 25 | issue = 6 | pages = 329–343 | date = July 1972 | pmid = 4650929 | doi = 10.1016/0021-9681(72)90027-6 }}</ref>

The interest in an index that measures [[body fat]] came with observed increasing obesity in prosperous [[Western world|Western]] societies. Keys explicitly judged BMI as appropriate for ''population'' studies and inappropriate for individual evaluation. Nevertheless, due to its simplicity, it has come to be widely used for preliminary diagnoses.<ref name=nhlbi>{{cite web|title= Assessing Your Weight and Health Risk|url= http://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm|publisher= National Heart, Lung and Blood Institute|access-date= 19 December 2014|url-status=live|archive-url= https://web.archive.org/web/20141219195703/http://www.nhlbi.nih.gov/health/educational/lose_wt/risk.htm|archive-date=19 December 2014|df= }}</ref> Additional metrics, such as waist circumference, can be more useful.<ref name=nhsob>{{cite web|title= Defining obesity|url= http://www.nhs.uk/Conditions/Obesity/Pages/Introduction.aspx|publisher= [[National Health Service|NHS]]|access-date= 19 December 2014|url-status=live|archive-url= https://web.archive.org/web/20141218121754/http://www.nhs.uk/Conditions/Obesity/Pages/Introduction.aspx|archive-date= 18 December 2014|df= }}</ref>

The BMI is universally expressed in kg/m<sup>2</sup>, resulting from mass in kilograms and height in metres. If pounds and inches are used, a conversion factor of 703&nbsp;(kg/m<sup>2</sup>)/(lb/in<sup>2</sup>) must be applied. When the term BMI is used informally, the units are usually omitted.

:<math>\mathrm{BMI} = \frac{\text{mass}_\text{kg}}{\text{height}_\text{m}^2}
= \frac{\text{mass}_\text{lb}}{\text{height}_\text{in}^2}\times 703</math>

BMI provides a simple numeric measure of a person's ''thickness'' or ''thinness'', allowing health professionals to discuss weight problems more objectively with their patients. BMI was designed to be used as a simple means of classifying average sedentary (physically inactive)  populations, with an average [[body composition]].<ref>
{{cite journal
 | vauthors = 
 | title = Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee
 | journal = World Health Organization Technical Report Series | volume = 854 | pages = 1–452
 | year = 1995 | pmid = 8594834 | url = http://whqlibdoc.who.int/trs/WHO_TRS_854.pdf
 | archive-url = https://web.archive.org/web/20070210134151/http://whqlibdoc.who.int/trs/WHO_TRS_854.pdf
 | df =  | url-status=live | archive-date = 2007-02-10 
}}
</ref>
For such individuals, the value recommendations {{as of | 2014 | lc = on}} are as follows: a BMI from 18.5 up to 25&nbsp;kg/m<sup>2</sup> may indicate optimal weight, a BMI lower than 18.5 suggests the person is [[underweight]], a number from 25 up to 30 may indicate the person is [[overweight]], and a number from 30 upwards suggests the person is [[obesity|obese]].<ref name=nhlbi /><ref name=nhsob /> Lean male athletes often have a high muscle-to-fat ratio and therefore a BMI that is misleadingly high relative to their body-fat percentage.<ref name=nhsob />

==Scalability==
BMI is proportional to the mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels. In comparison, the [[Ponderal index]] is based on the natural scaling of mass with the third power of the height.{{fact|date=November 2019}}

However, many taller people are not just "scaled up" short people but tend to have narrower frames in proportion to their height. Carl Lavie has written that, "The B.M.I. tables are excellent for identifying obesity and body fat in large populations, but they are far less reliable for determining fatness in individuals."<ref>{{cite web|url=https://www.nytimes.com/2010/08/31/health/31brod.html|title=Weight Index Doesn't Tell the Whole Truth|date=31 August 2010|work=The New York Times|url-status=live|archive-url=https://web.archive.org/web/20170501153306/http://www.nytimes.com/2010/08/31/health/31brod.html|archive-date=1 May 2017|df=}}</ref>

==Categories==
A frequent use of the BMI is to assess how far an individual's body weight departs from what is normal or desirable for a person's height. The weight excess or deficiency may, in part, be accounted for by body fat ([[adipose tissue]]) although other factors such as muscularity also affect BMI significantly (see discussion below and [[overweight]]).<ref>{{Cite web|url=https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html|title=About Adult BMI {{!}} Healthy Weight {{!}} CDC|date=2017-08-29|website=www.cdc.gov|language=en-us|access-date=2018-01-26}}</ref>

The [[World Health Organization|WHO]] regards a BMI of less than 18.5 as underweight and may indicate [[malnutrition]], an [[eating disorder]], or other health problems, while a BMI equal to or greater than 25 is considered overweight and above 30 is considered [[obesity|obese]].<ref name="BMI Classification">{{cite web |url=http://www.who.int/bmi/index.jsp?introPage=intro_3.html |title=BMI Classification |work=Global Database on Body Mass Index |publisher=World Health Organization |year=2006 |access-date=July 27, 2012 |url-status=live |archive-url=https://web.archive.org/web/20090418181049/http://www.who.int/bmi/index.jsp?introPage=intro_3.html |archive-date=April 18, 2009 |df= }}</ref> These ranges of BMI values are valid only as statistical categories.

{| class="wikitable"
|-
! Category
! colspan="2"| BMI (kg/m<sup>2</sup>)
! colspan="2"| BMI Prime<br>{{clarify|date=October 2019}}
|-
|
! from || to
! from || to
|-
| Very severely underweight
|      || 15
|      || 0.60
|-
| Severely underweight
| 15 || 16
| 0.60 || 0.64
|-
| Underweight
| 16 || 18.5
| 0.64 || 0.74
|-
| Normal (healthy weight)
| 18.5 || 25
| 0.74 || 1.0
|-
| Overweight
| 25  || 30
| 1.0 || 1.2
|-
| Obese Class I (Moderately obese)
| 30  || 35
| 1.2 || 1.4
|-
| Obese Class II (Severely obese)
| 35  || 40
| 1.4 || 1.6
|-
| Obese Class III (Very severely obese)
| 40  || 45
| 1.6 || 1.8
|-
| Obese Class IV (Morbidly obese)
| 45 || 50
| 1.8 || 2
|-
| Obese Class V (Super obese)
| 50 || 60
| 2 || 2.4
|-
| Obese Class VI (Hyper obese)
| 60 ||
| 2.4 ||
<!--
| Very Severely Obese
| from 40 to 45
| from 1.6 to 1.8
|-
| Morbidly Obese
| from 45 to 50
| from 1.8 to 2.0
|-
| Super Obese
| from 50 to 60
| from 2.0 to 2.4
|-
| Hyper Obese
| from 60
| from 2.4-->
|}

===Children (aged 2 to 20)===
[[File:BMIBoys 1.svg|thumb|BMI for age percentiles for boys 2 to 20 years of age.]]
[[File:BMIGirls 1.svg|thumb|BMI for age percentiles for girls 2 to 20 years of age.]]
BMI is used differently for children. It is calculated in the same way as for adults, but then compared to typical values for other children of the same age. Instead of comparison against fixed thresholds for underweight and overweight, the BMI is compared against the [[percentile]]s for children of the same sex and age.<ref>{{cite web|url = https://www.cdc.gov/nccdphp/dnpa/healthyweight/assessing/bmi/childrens_BMI/about_childrens_BMI.htm|title = Body Mass Index: BMI for Children and Teens|publisher = Center for Disease Control|access-date = 2013-12-16|url-status=live|archive-url = https://web.archive.org/web/20131029061522/http://www.cdc.gov/nccdphp/dnpa/healthyweight/assessing/bmi/childrens_BMI/about_childrens_BMI.htm|archive-date = 2013-10-29|df = }}</ref>

A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered obese. Children with a BMI between the 85th and 95th percentile are considered to be overweight.<ref>{{cite book | chapter = Chapter 2: Use of Percentiles and Z-Scores in Anthropometry | title = Handbook of Anthropometry|last=Wang|first=Youfa| name-list-format = vanc |publisher=Springer|year=2012|isbn=978-1-4419-1787-4|location=New York|pages=29}}</ref>

Recent studies in Britain have indicated that females between the ages 12 and 16 have a higher BMI than males of the same age by 1.0&nbsp;kg/m<sup>2</sup> on average.<ref>{{cite web|url = http://www.archive2.official-documents.co.uk/document/deps/doh/survey02/summ03.htm|title = Health Survey for England: The Health of Children and Young People|website = Archive2.official-documents.co.uk|access-date = 16 December 2013|url-status=dead|archive-url = https://web.archive.org/web/20120625003857/http://www.archive2.official-documents.co.uk/document/deps/doh/survey02/summ03.htm|archive-date = 2012-06-25|df = }}</ref>

===International variations===
These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic. People from different ethnic groups, populations, and descent have different associations between BMI, percentage of body fat, and health risks, with a higher risk of [[type 2 diabetes mellitus]] and [[Atherosclerosis|atherosclerotic]] cardiovascular disease at BMIs lower than the [[World Health Organization|WHO]] cut-off point for overweight, 25&nbsp;kg/m<sup>2</sup>, although the cut-off for observed risk varies among different populations. The cut-off for observed risk varies based on populations and subpopulations both in Europe and Asia.<ref>{{cite journal | title = Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies | journal = Lancet | volume = 363 | issue = 9403 | pages = 157–163 | date = January 2004 | pmid = 14726171 | doi = 10.1016/S0140-6736(03)15268-3 | author1 = WHO Expert Consultation }}{{Open access}}</ref>

====Hong Kong====
The [[Hospital Authority]] of [[Hong Kong]] recommends the use of the following BMI ranges:<ref name="ha">{{cite web|url=https://www.fitnessofbody.com/2019/04/body-weight-chart.html|title=Body weight chart - ideal goal weight chart|last=|first=|date=|publisher=Fitness of Body - Health & Wellness site|language=en|archive-url=|archive-date=|url-status=|access-date=}}</ref>

{| class="wikitable"
|-
! Category
! colspan="2"| BMI (kg/m<sup>2</sup>)
|-
|
! from || to
|-
| Underweight
|     || 18.5
|-
| Normal Range
| 18.5 || 23
|-
| Overweight—At Risk
| 23   || 25
|-
| Overweight—Moderately Obese
| 25   || 30
|-
| Overweight—Severely Obese
| 30 ||
|}

====Japan====

Japan Society for the Study of Obesity (2000):<ref name="himan-mhlw">{{cite web |url=http://www.mhlw.go.jp/topics/bukyoku/kenkou/seikatu/himan/about.html |title={{as written|肥満って、 どんな状態？}} |trans-title=What is obesity, what kind of state? |work=Obesity Homepage<!--肥満ホームページ--> |publisher=Ministry of Health, Labor and Welfare<!--厚生労働省--> |access-date=2013-05-25 |language=ja |url-status=dead |archive-url=https://web.archive.org/web/20130628232937/http://www.mhlw.go.jp/topics/bukyoku/kenkou/seikatu/himan/about.html |archive-date=2013-06-28 |df= }}</ref>

{| class="wikitable"
|-
! Category
! colspan="2"| BMI (kg/m<sup>2</sup>)
|-
|
| from || to
|-
| Low
|     || 18.5
|-
| Normal
| 18.5 || 25
|-
|Obese (Level 1)
| 25 || 30
|-
|Obese (Level 2)
| 30 || 35
|-
|Obese (Level 3)
| 35 || 40
|-
|Obese (Level 4)
| 40 || 
|}
<ref>{{cite journal | vauthors = Shiwaku K, Anuurad E, Enkhmaa B, Nogi A, Kitajima K, Shimono K, Yamane Y, Oyunsuren T | title = Overweight Japanese with body mass indexes of 23.0–24.9 have higher risks for obesity-associated disorders: a comparison of Japanese and Mongolians | journal = International Journal of Obesity and Related Metabolic Disorders | volume = 28 | issue = 1 | pages = 152–158 | date = January 2004 | pmid = 14557832 | doi = 10.1038/sj.ijo.0802486 | displayauthors = 6 }}</ref>{{clarify|date=March 2013}}

====Singapore====
In Singapore, the BMI cut-off figures were revised in 2005, motivated by studies showing that many Asian populations, including Singaporeans, have higher proportion of body fat and increased risk for cardiovascular diseases and [[diabetes mellitus]], compared with general BMI recommendations in other countries. The BMI cut-offs are presented with an emphasis on health risk rather than weight.

{| class="wikitable"
|-
! Health Risk
! colspan="2"| BMI (kg/m<sup>2</sup>)
|-
| Risk of developing problems such as nutritional deficiency and osteoporosis
| under 18.5
|-
| Low Risk (healthy range)
| 18.5 to 23
|-
| Moderate risk of developing heart disease, high blood pressure, stroke, diabetes
| 23 to 27.5
|-
| High risk of developing heart disease, high blood pressure, stroke, diabetes
| over 27.5
|}

====United States====
In 1998, the U.S. [[National Institutes of Health]] and the [[Centers for Disease Control and Prevention]] brought U.S. definitions in line with [[World Health Organization]] guidelines, lowering the normal/overweight cut-off from BMI 27.8 to BMI 25. This had the effect of redefining approximately 29 million Americans, previously ''healthy'', to ''overweight''.<ref>{{cite news | url=http://www.cnn.com/HEALTH/9806/17/weight.guidelines/ | title=Who's fat? New definition adopted | publisher=CNN | date=June 17, 1998 | access-date=2010-04-26 | url-status=live | archive-url=https://web.archive.org/web/20101122173108/http://www.cnn.com/HEALTH/9806/17/weight.guidelines/ | archive-date=November 22, 2010 | df= }}</ref>

This can partially explain the increase in the ''overweight'' diagnosis in the past 20 years, and the increase in sales of weight loss products during the same time. [[World Health Organization|WHO]] also recommends lowering the normal/overweight threshold for South East Asian body types to around BMI 23, and expects further revisions to emerge from clinical studies of different body types.<ref>{{Cite journal|last=World Health Organization|date=January 10, 2004|title=Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies|url=http://www.who.int/nutrition/publications/bmi_asia_strategies.pdf|journal=The Lancet|volume=363|issue=9403|pages=157–163|doi=10.1016/s0140-6736(03)15268-3|pmid=14726171|via=}}</ref>

The U.S. National Health and Nutrition Examination Survey of 1994 showed that 59.8% of American men and 51.2% of women had BMIs over 25.<ref>{{cite web|url=https://www.cdc.gov/nchs/data/nhanes/databriefs/adultweight.pdf|title=Healthy weight, overweight, and obesity among U.S. adults|url-status=live|archive-url=https://web.archive.org/web/20160513072652/http://www.cdc.gov/nchs/data/nhanes/databriefs/adultweight.pdf|archive-date=2016-05-13|df=}}</ref> Morbid obesity—a BMI of 40 or more—was found in 2% of the men and 4% of the women. A survey in 2007 showed 63% of Americans are overweight or obese, with 26% in the obese category (a BMI of 30 or more). {{as of|2014}}, 37.7% of adults in the United States were obese, categorized as 35.0% of men and 40.4% of women; class 3 obesity (BMI over 40) values were 7.7% for men and 9.9% for women.<ref>{{cite journal | vauthors = Flegal KM, Kruszon-Moran D, Carroll MD, Fryar CD, Ogden CL | title = Trends in Obesity Among Adults in the United States, 2005 to 2014 | journal = JAMA | volume = 315 | issue = 21 | pages = 2284–2291 | date = June 2016 | pmid = 27272580 | doi = 10.1001/jama.2016.6458 }}</ref>

{| class="wikitable" style="font-size: small;"
|-
|+ Body Mass Index values for males and females aged 20 and over, and selected percentiles by age: United States, 2011–2014.<ref>{{cite web|url=https://www.cdc.gov/nchs/data/series/sr_03/sr03_039.pdf|title=Anthropometric Reference Data for Children and Adults: United States|publisher=[[Centers for Disease Control and Prevention|CDC DHHS]]|date=2016|url-status=live|archive-url=https://web.archive.org/web/20170202010330/https://www.cdc.gov/nchs/data/series/sr_03/sr03_039.pdf|archive-date=2017-02-02|df=}}</ref>
|-
! rowspan=3 | Age
! colspan=9 | Percentile
|-
! 5th
! 10th
! 15th
! 25th
! 50th
! 75th
! 85th
! 90th
! 95th
|-
! colspan=9 | Men BMI (kg/m<sup>2</sup>)
|-
| 20 years and over (total)
| 20.7
| 22.2
| 23.0
| 24.6
| 27.7
| 31.6
| 34.0
| 36.1
| 39.8
|-
| 20–29 years
| 19.3
| 20.5
| 21.2
| 22.5
| 25.5
| 30.5
| 33.1
| 35.1
| 39.2
|-
| 30–39 years
| 21.1
| 22.4
| 23.3
| 24.8
| 27.5
| 31.9
| 35.1
| 36.5
| 39.3
|-
| 40–49 years
| 21.9
| 23.4
| 24.3
| 25.7
| 28.5
| 31.9
| 34.4
| 36.5
| 40.0
|-
| 50–59 years
| 21.6
| 22.7
| 23.6
| 25.4
| 28.3
| 32.0
| 34.0
| 35.2
| 40.3
|-
| 60–69 years
| 21.6
| 22.7
| 23.6
| 25.3
| 28.0
| 32.4
| 35.3
| 36.9
| 41.2
|-
| 70–79 years
| 21.5
| 23.2
| 23.9
| 25.4
| 27.8
| 30.9
| 33.1
| 34.9
| 38.9
|-
| 80 years and over
| 20.0
| 21.5
| 22.5
| 24.1
| 26.3
| 29.0
| 31.1
| 32.3
| 33.8
|-
! Age
! colspan=9 | Women BMI (kg/m<sup>2</sup>)
|-
| 20 years and over (total)
| 19.6
| 21.0
| 22.0
| 23.6
| 27.7
| 33.2
| 36.5
| 39.3
| 43.3
|-
| 20–29 years
| 18.6
| 19.8
| 20.7
| 21.9
| 25.6
| 31.8
| 36.0
| 38.9
| 42.0
|-
| 30–39 years
| 19.8
| 21.1
| 22.0
| 23.3
| 27.6
| 33.1
| 36.6
| 40.0
| 44.7
|-
| 40–49 years
| 20.0
| 21.5
| 22.5
| 23.7
| 28.1
| 33.4
| 37.0
| 39.6
| 44.5
|-
| 50–59 years
| 19.9
| 21.5
| 22.2
| 24.5
| 28.6
| 34.4
| 38.3
| 40.7
| 45.2
|-
| 60–69 years
| 20.0
| 21.7
| 23.0
| 24.5
| 28.9
| 33.4
| 36.1
| 38.7
| 41.8
|-
| 70–79 years
| 20.5
| 22.1
| 22.9
| 24.6
| 28.3
| 33.4
| 36.5
| 39.1
| 42.9
|-
| 80 years and over
| 19.3
| 20.4
| 21.3
| 23.3
| 26.1
| 29.7
| 30.9
| 32.8
| 35.2
|}

==Consequences of elevated level in adults==
The BMI ranges are based on the relationship between body weight and disease and death.<ref>{{cite journal | vauthors = <!--Staff writer(s); no by-line.--> | title = Physical status: the use and interpretation of anthropometry. Report of a WHO Expert Committee | journal = World Health Organization Technical Report Series | volume = 854 | issue = 854 | pages = 1–452 | year = 1995 | pmid = 8594834 | url = <!-- derived from:http://www.who.int/childgrowth/publications/physical_status/en/-->http://whqlibdoc.who.int/trs/WHO_TRS_854.pdf | archive-url = https://web.archive.org/web/20070210134151/http://whqlibdoc.who.int/trs/WHO_TRS_854.pdf | df =  | url-status=live | archive-date = 2007-02-10 }}</ref> Overweight and obese individuals are at an increased risk for the following diseases:<ref>{{cite book |chapter=Executive Summary |chapterurl=https://www.ncbi.nlm.nih.gov/books/NBK2008/ |pages=xi–xxx |nopp=y |date=September 1998 |title=Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report |url=http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm |publisher=[[National Heart, Lung, and Blood Institute]] |url-status=live |archive-url=https://web.archive.org/web/20130103083355/http://www.nhlbi.nih.gov/guidelines/obesity/ob_gdlns.htm |archive-date=2013-01-03 |df= }}</ref>
* [[Coronary artery disease]]
* [[Dyslipidemia]]
* [[Diabetes mellitus type 2|Type 2 diabetes]]
* [[Gallbladder disease]]
* [[Hypertension]]
* [[Osteoarthritis]]
* [[Sleep apnea]]
* [[Stroke]]
* At least 10 cancers, including [[Endometrial cancer|endometrial]], [[Breast cancer|breast]], and [[colon cancer]].<ref>{{cite journal | vauthors = Bhaskaran K, Douglas I, Forbes H, dos-Santos-Silva I, Leon DA, Smeeth L | title = Body-mass index and risk of 22 specific cancers: a population-based cohort study of 5·24 million UK adults | journal = Lancet | volume = 384 | issue = 9945 | pages = 755–765 | date = August 2014 | pmid = 25129328 | pmc = 4151483 | doi = 10.1016/S0140-6736(14)60892-8 | url = http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(14)60892-8/fulltext }}</ref>
* Epidural [[lipomatosis]] <ref>{{cite journal|title=Multiple epidural steroid injections and body mass index linked with occurrence of epidural lipomatosis: a case series| doi=10.1186/1471-2253-14-70|pmid = 25183952| pmc=4145583|volume=14| pages=70|year=2014|journal=BMC Anesthesiology|author=Jaimes R, Rocco AG}}</ref>

Among people who have never smoked, overweight/obesity is associated with 51% increase in mortality compared with people who have always been a normal weight.<ref>{{cite journal | vauthors = Stokes A, Preston SH | title = Smoking and reverse causation create an obesity paradox in cardiovascular disease | journal = Obesity | volume = 23 | issue = 12 | pages = 2485–2490 | date = December 2015 | pmid = 26421898 | pmc = 4701612 | doi = 10.1002/oby.21239 | df =  }}</ref>

==Applications==

===Public health===
The BMI is generally used as a means of correlation between groups related by general mass and can serve as a vague means of estimating [[adipose tissue|adiposity]]. The duality of the BMI is that, while it is easy to use as a general calculation, it is limited as to how accurate and pertinent the data obtained from it can be. Generally, the index is suitable for recognizing trends within sedentary or overweight individuals because there is a smaller margin of error.<ref name="jxbvhf">{{cite book |last1=Jeukendrup |first1=A. |authorlink1=Asker Jeukendrup |last2=Gleeson |first2=M. | name-list-format = vanc |year=2005 |title=Sports Nutrition |publisher=Human Kinetics: An Introduction to Energy Production and Performance |isbn=978-0-7360-3404-3}}{{page needed|date=April 2012}}</ref> The BMI has been used by the [[World Health Organization|WHO]] as the standard for recording obesity statistics since the early 1980s.

This general correlation is particularly useful for consensus data regarding obesity or various other conditions because it can be used to build a semi-accurate representation from which a solution can be stipulated, or the [[Recommended Dietary Allowance|RDA]] for a group can be calculated. Similarly, this is becoming more and more pertinent to the growth of children, due to the fact that the majority of children are sedentary.<ref>{{cite book |last=Barasi |first=M. E. | name-list-format = vanc |year=2004 |title=Human Nutrition – a health perspective |isbn=978-0-340-81025-5}}{{page needed|date=April 2012}}</ref>
Cross-sectional studies indicated that sedentary people can decrease BMI by becoming more physically active. Smaller effects are seen in prospective cohort studies which lend to support active mobility as a means to prevent a further increase in BMI.<ref name="Dons">{{cite journal
  | last = Dons
  | first = E
  | title = Transport mode choice and body mass index: Cross-sectional and longitudinal evidence from a European-wide study
  | journal = Environment International
  | volume =  119
 | issue = 119
  | pages = 109–116
  | year = 2018
  | doi =  10.1016/j.envint.2018.06.023
  | pmid = 29957352
| url = http://spiral.imperial.ac.uk/bitstream/10044/1/61061/2/Dons2018%20preprint_BMI.pdf
  }}</ref>

===Clinical practice===
BMI categories are generally regarded as a satisfactory tool for measuring whether sedentary individuals are ''underweight'', ''overweight'', or ''obese'' with various exceptions, such as: athletes, children, the elderly, and the infirm.{{Citation needed|date=May 2013}} Also, the growth of a child is documented against a BMI-measured growth chart. Obesity trends can then be calculated from the difference between the child's BMI and the BMI on the chart.{{Citation needed|date=April 2011}} In the United States, BMI is also used as a measure of underweight, owing to advocacy on behalf of those with eating disorders, such as [[anorexia nervosa]] and [[bulimia nervosa]].{{Citation needed|date=April 2007}}

===Legislation===
In France, Italy, and Spain, legislation has been introduced banning the usage of fashion show models having a BMI below 18.<ref>{{cite web|url=http://time.com/3770696/france-banned-ultra-thin-models/|title=France Just Banned Ultra-Thin Models|author=Laura Stampler|work=TIME.com|url-status=live|archive-url=https://web.archive.org/web/20150410084813/http://time.com/3770696/france-banned-ultra-thin-models/|archive-date=2015-04-10|df=}}</ref> In Israel, a BMI below 18.5 is banned.<ref>{{cite web|url=http://abcnews.go.com/International/israeli-law-bans-skinny-bmi-challenged-models/story?id=18116291|title=Israeli Law Bans Skinny, BMI-Challenged Models|author=ABC News|work=ABC News|url-status=live|archive-url=https://web.archive.org/web/20141210120342/http://abcnews.go.com/International/israeli-law-bans-skinny-bmi-challenged-models/story?id=18116291|archive-date=2014-12-10|df=}}</ref> This is done to fight [[Anorexia nervosa|anorexia]] among models and people interested in fashion.

==Limitations==
[[File:Correlation between BMI and Percent Body Fat for Men in NCHS' NHANES 1994 Data.PNG|right|395px|thumb|This graph shows the correlation between body mass index (BMI) and percent body fat (%BF) for 8550 men in [[National Center for Health Statistics|NCHS]]' [[National Health and Nutrition Examination Survey|NHANES]] 1994 data. Data in the upper left and lower right quadrants suggest the limitations of BMI.<ref name="RomeroCorral2008">{{cite journal | vauthors = Romero-Corral A, Somers VK, Sierra-Johnson J, Thomas RJ, Collazo-Clavell ML, Korinek J, Allison TG, Batsis JA, Sert-Kuniyoshi FH, Lopez-Jimenez F | title = Accuracy of body mass index in diagnosing obesity in the adult general population | journal = International Journal of Obesity | volume = 32 | issue = 6 | pages = 959–966 | date = June 2008 | pmid = 18283284 | pmc = 2877506 | doi = 10.1038/ijo.2008.11 | displayauthors = 6 }}</ref>]]
The medical establishment<ref>{{cite web |url=http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations |title=Aim for a Healthy Weight: Assess your Risk |publisher=National Institutes of Health |date=July 8, 2007 |access-date=15 December 2013 |url-status=live |archive-url=https://web.archive.org/web/20131216071225/http://www.nhlbi.nih.gov/health/public/heart/obesity/lose_wt/risk.htm#limitations |archive-date=16 December 2013 |df= }}</ref> and statistical community<ref>{{cite journal | vauthors = Kronmal RA | year = 1993 | title = Spurious correlation and the fallacy of the ratio standard revisited | journal = Journal of the Royal Statistical Society | volume = 156 | issue = 3| pages = 379–392 | doi = 10.2307/2983064 | jstor = 2983064 }}</ref> have both highlighted the limitations of BMI.

===Scaling===
The exponent in the denominator of the formula for BMI is arbitrary. The BMI depends upon weight and the ''square'' of height. Since mass increases to the ''third power'' of linear dimensions, taller individuals with exactly the same body shape and relative composition have a larger BMI.<ref>{{cite journal | vauthors = Taylor RS | title = Letter to the editor | journal = Paediatrics & Child Health | volume = 15 | issue = 5 | pages = 258 | date = May 2010 | pmid = 21532785 | pmc = 2912631 | doi=10.1093/pch/15.5.258}}</ref>

According to mathematician [[Lloyd N. Trefethen|Nick Trefethen]], "BMI divides the weight by too large a number for short people and too small a number for tall people. So short people are misled into thinking that they are thinner than they are, and tall people are misled into thinking they are fatter."<ref>{{cite news|url=https://www.telegraph.co.uk/news/health/news/9815052/Short-people-fatter-than-they-think-under-new-BMI.html|title=Short people 'fatter than they think' under new BMI|date=21 January 2013|work=Telegraph.co.uk|url-status=live|archive-url=https://web.archive.org/web/20150823193248/http://www.telegraph.co.uk/news/health/news/9815052/Short-people-fatter-than-they-think-under-new-BMI.html|archive-date=23 August 2015|df=|last1=Reporters|first1=Telegraph}}</ref>

For US adults, exponent estimates range from 1.92 to 1.96 for males and from 1.45 to 1.95 for females.<ref>{{cite journal | title = Weight-height relationships and body mass index: some observations from the Diverse Populations Collaboration | journal = American Journal of Physical Anthropology | volume = 128 | issue = 1 | pages = 220–229 | date = September 2005 | pmid = 15761809 | doi = 10.1002/ajpa.20107 | author1 = Diverse Populations Collaborative Group }}</ref><ref>{{cite journal | vauthors = Levitt DG, Heymsfield SB, Pierson RN, Shapses SA, Kral JG | title = Physiological models of body composition and human obesity | journal = Nutrition & Metabolism | volume = 4 | pages = 19 | date = September 2007 | pmid = 17883858 | pmc = 2082278 | doi = 10.1186/1743-7075-4-19 }}</ref>

===Physical characteristics===
The BMI overestimates roughly 10% for a large (or tall) frame and underestimates roughly 10% for a smaller frame (short stature). In other words, persons with small frames would be carrying more fat than optimal, but their BMI indicates that they are ''normal''. Conversely, large framed (or tall) individuals may be quite healthy, with a fairly low [[body fat percentage]], but be classified as ''overweight'' by BMI.<ref>{{cite web|url=http://www.medicalnewstoday.com/articles/265215.php|title=Why BMI is inaccurate and misleading|work=Medical News Today|url-status=live|archive-url=https://web.archive.org/web/20150723131349/http://www.medicalnewstoday.com/articles/265215.php|archive-date=2015-07-23}}</ref>

For example, a height/weight chart may say the ideal weight (BMI 21.5) for a man {{convert|5|ft|10|in|cm|abbr=on}} is {{convert|150|lb|kg}}. But if that man has a slender build (small frame), he may be overweight at {{convert|150|lb|kg}} and should reduce by 10%, to roughly {{convert|135|lb|kg}} (BMI 19.4). In the reverse, the man with a larger frame and more solid build should increase by 10%, to roughly {{convert|165|lb|kg}} (BMI 23.7). If one teeters on the edge of small/medium or medium/large, common sense should be used in calculating one's ideal weight. However, falling into one's ideal weight range for height and build is still not as accurate in determining health risk factors as [[waist-to-height ratio]] and actual body fat percentage.<ref>{{cite web|url=http://www.medicalnewstoday.com/articles/255712.php|title=BMI: is the body mass index formula flawed?|work=Medical News Today|url-status=live|archive-url=https://web.archive.org/web/20150723095030/http://www.medicalnewstoday.com/articles/255712.php|archive-date=2015-07-23|df=}}</ref>

Accurate frame size calculators use several measurements (wrist circumference, elbow width, neck circumference and others) to determine what category an individual falls into for a given height.<ref>{{cite web|url=http://www.livescience.com/39097-bmi-not-accurate-health-measure.html|title=BMI Not a Good Measure of Healthy Body Weight, Researchers Argue|work=LiveScience.com|url-status=live|archive-url=https://web.archive.org/web/20150721123646/http://www.livescience.com/39097-bmi-not-accurate-health-measure.html|archive-date=2015-07-21|df=}}</ref> The BMI also fails to take into account loss of height through aging. In this situation, BMI will increase without any corresponding increase in weight.

A new formula, that accounts for the distortions of BMI at high and low heights, has been suggested: BMI = 1.3*weight(kg)/height(m)^2.5<ref>{{cite web |last1=Nick |first1=Trefethen |title=New BMI (New Body Mass Index) |url=https://people.maths.ox.ac.uk/trefethen/bmi.html |website=Numerical analysis |publisher=University of Oxford |accessdate=5 February 2019}}</ref>

===Muscle versus fat===
Assumptions about the distribution between muscle mass and fat mass are inexact. BMI generally overestimates [[adipose tissue|adiposity]] on those with more lean body mass (e.g., athletes) and underestimates excess adiposity on those with less lean body mass.

A study in June 2008 by Romero-Corral et al. examined 13,601 subjects from the United States' third [[National Health and Nutrition Examination Survey]] (NHANES III) and found that BMI-defined obesity (BMI > 30) was present in 21% of men and 31% of women. Body fat-defined obesity was found in 50% of men and 62% of women. While BMI-defined obesity showed high [[Sensitivity and specificity|specificity]] (95% for men and 99% for women), BMI showed poor [[Sensitivity and specificity|sensitivity]] (36% for men and 49% for women). In other words, BMI is better at determining a person is not obese than it is at determining a person is obese. Despite this undercounting of obesity by BMI, BMI values in the intermediate BMI range of 20–30 were found to be associated with a wide range of body fat percentages. For men with a BMI of 25, about 20% have a body fat percentage below 20% and about 10% have body fat percentage above 30%.<ref name="RomeroCorral2008"/>

BMI is particularly inaccurate for people who are very fit or athletic, as their high muscle mass can classify them in the ''overweight'' category by BMI, even though their body fat percentages frequently fall in the 10–15% category, which is below that of a more sedentary person of average build who has a ''normal'' BMI number.{{Citation needed|date=July 2017}} For example, the BMI of bodybuilder and eight-time [[Mr. Olympia]] [[Ronnie Coleman]] was 41.8 at his peak physical condition, which would be considered [[Classification of obesity|morbidly obese]].<ref>Ronnie Coleman is 5'11" tall and weighed 300 lbs during competition. {{cite web|title=Ronnie Coleman Pro Bodybuilding Profile, Bodybuilding.com|date=July 22, 2013|url=https://www.bodybuilding.com/fun/bodybuilders-ronnie.htm}}</ref>  Body composition for athletes is often better calculated using measures of body fat, as determined by such techniques as skinfold measurements or underwater weighing and the limitations of manual measurement have also led to new, alternative methods to measure obesity, such as the [[body volume index]].

===Variation in definitions of categories===
It is not clear where on the BMI scale the threshold for ''[[overweight]]'' and ''[[obesity|obese]]'' should be set. Because of this the standards have varied over the past few decades. Between 1980 and 2000 the U.S. Dietary Guidelines have defined overweight at a variety of levels ranging from a BMI of 24.9 to 27.1. In 1985 the [[National Institutes of Health]] (NIH) consensus conference recommended that overweight BMI be set at a BMI of 27.8 for men and 27.3 for women.

In 1998 a NIH report concluded that a BMI over 25 is overweight and a BMI over 30 is obese.<ref>{{cite web |url=http://edition.cnn.com/HEALTH/9806/17/weight.guidelines/ |title=Who's fat? New definition adopted |date=June 17, 1998 |access-date=2014-07-15 |url-status=live |archive-url=https://web.archive.org/web/20140515082415/http://edition.cnn.com/HEALTH/9806/17/weight.guidelines/ |archive-date=May 15, 2014 |df= }}</ref> In the 1990s the [[World Health Organization]] (WHO) decided that a BMI of 25 to 30 should be considered overweight and a BMI over 30 is obese, the standards the NIH set. This became the definitive guide for determining if someone is overweight.

The current WHO and NIH ranges of ''normal'' weights are proved to be associated with decreased risks of some diseases such as diabetes type II; however using the same range of BMI for men and women is considered arbitrary, and makes the definition of underweight quite unsuitable for men.<ref>{{cite web|url=http://www.halls.md/ideal-weight/medical.htm|title=Ideal Weight and definition of Overweight|author=Halls|work=Moose and Doc|url-status=live|archive-url=https://web.archive.org/web/20110126140124/http://halls.md/ideal-weight/medical.htm|archive-date=2011-01-26|df=|date=2019-02-18}}</ref>

One study found that the vast majority of people labelled 'overweight' and 'obese' according to current definitions do not in fact face any meaningful increased risk for early death. In a quantitative analysis of a number of studies, involving more than 600,000 men and women, the lowest mortality rates were found for people with BMIs between 23 and 29; most of the 25–30 range considered 'overweight' was not associated with higher risk.<ref>{{cite journal | vauthors = Campos P, Saguy A, Ernsberger P, Oliver E, Gaesser G | title = The epidemiology of overweight and obesity: public health crisis or moral panic? | journal = International Journal of Epidemiology | volume = 35 | issue = 1 | pages = 55–60 | date = February 2006 | pmid =  16339599| doi = 10.1093/ije/dyi254 | access-date =  }}</ref>

===Relationship to health===
A study published by ''[[Journal of the American Medical Association]]'' (''JAMA'') in 2005 showed that ''overweight'' people had a death rate similar to ''normal'' weight people as defined by BMI, while ''underweight'' and ''obese'' people had a higher death rate.<ref>{{cite journal | vauthors = Flegal KM, Graubard BI, Williamson DF, Gail MH | title = Excess deaths associated with underweight, overweight, and obesity | journal = JAMA | volume = 293 | issue = 15 | pages = 1861–1867 | date = April 2005 | pmid = 15840860 | doi = 10.1001/jama.293.15.1861 }}</ref>

A study published by ''[[The Lancet]]'' in 2009 involving 900,000 adults showed that ''overweight'' and ''underweight'' people both had a mortality rate higher than ''normal'' weight people as defined by BMI. The optimal BMI was found to be in the range of 22.5–25.<ref>{{cite journal | vauthors = Whitlock G, Lewington S, Sherliker P, Clarke R, Emberson J, Halsey J, Qizilbash N, Collins R, Peto R | title = Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies | journal = Lancet | volume = 373 | issue = 9669 | pages = 1083–1096 | date = March 2009 | pmid = 19299006 | pmc = 2662372 | doi = 10.1016/S0140-6736(09)60318-4 | url = http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(09)60318-4/fulltext | access-date = July 11, 2016 }}</ref>

High BMI is associated with [[diabetes mellitus type 2|type&nbsp;2 diabetes]] only in persons with high serum [[gamma-glutamyl transpeptidase]].<ref name="pmid21976023">{{cite journal | vauthors = Lim JS, Lee DH, Park JY, Jin SH, Jacobs DR | title = A strong interaction between serum gamma-glutamyltransferase and obesity on the risk of prevalent type 2 diabetes: results from the Third National Health and Nutrition Examination Survey | journal = Clinical Chemistry | volume = 53 | issue = 6 | pages = 1092–1098 | date = June 2007 | pmid = 17478563 | doi = 10.1373/clinchem.2006.079814 | df =  }}</ref>

In an analysis of 40 studies involving 250,000 people, patients with coronary artery disease with ''normal'' BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the ''overweight'' range (BMI 25–29.9).<ref>{{cite journal | vauthors = Romero-Corral A, Montori VM, Somers VK, Korinek J, Thomas RJ, Allison TG, Mookadam F, Lopez-Jimenez F | title = Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: a systematic review of cohort studies | journal = Lancet | volume = 368 | issue = 9536 | pages = 666–678 | date = August 2006 | pmid = 16920472 | doi = 10.1016/S0140-6736(06)69251-9 }}</ref>

One study found that BMI had a good general correlation with body fat percentage, and noted that obesity has overtaken smoking as the world's number one cause of death. But it also notes that in the study 50% of men and 62% of women were obese according to body fat defined obesity, while only 21% of men and 31% of women were obese according to BMI, meaning that BMI was found to underestimate the number of obese subjects.<ref name="RomeroCorral2008"/>

A 2010 study that followed 11,000 subjects for up to eight years concluded that BMI is not a good measure for the risk of heart attack, stroke or death. A better measure was found to be the [[waist-to-height ratio]].<ref>{{cite journal | vauthors = Schneider HJ, Friedrich N, Klotsche J, Pieper L, Nauck M, John U, Dörr M, Felix S, Lehnert H, Pittrow D, Silber S, Völzke H, Stalla GK, Wallaschofski H, Wittchen HU | title = The predictive value of different measures of obesity for incident cardiovascular events and mortality | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 95 | issue = 4 | pages = 1777–1785 | date = April 2010 | pmid = 20130075 | doi = 10.1210/jc.2009-1584 | displayauthors = 6 }}</ref> A 2011 study that followed 60,000 participants for up to 13 years found that [[waist–hip ratio]] was a better predictor of ischaemic heart disease mortality.<ref name= "MørkedalRomundstad2011">{{cite journal | vauthors = Mørkedal B, Romundstad PR, Vatten LJ | title = Informativeness of indices of blood pressure, obesity and serum lipids in relation to ischaemic heart disease mortality: the HUNT-II study | journal = European Journal of Epidemiology | volume = 26 | issue = 6 | pages = 457–461 | date = June 2011 | pmid = 21461943 | pmc = 3115050 | doi = 10.1007/s10654-011-9572-7 }}</ref>

==Alternatives==

===BMI Prime===
BMI Prime, a modification of the BMI system, is the ratio of actual BMI to upper limit optimal BMI (currently defined at 25&nbsp;kg/m<sup>2</sup>), i.e., the actual BMI expressed as a proportion of upper limit optimal. The ratio of actual body weight to body weight for upper limit optimal BMI (25&nbsp;kg/m<sup>2</sup>) is equal to BMI Prime. BMI Prime is a [[dimensionless number]] independent of units. Individuals with BMI Prime less than 0.74 are underweight; those with between 0.74 and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI Prime is useful clinically because it shows by what ratio (e.g. 1.36) or percentage (e.g. 136%, or 36% above) a person deviates from the maximum optimal BMI.

For instance, a person with BMI 34&nbsp;kg/m<sup>2</sup> has a BMI Prime of 34/25 = 1.36, and is 36% over their upper mass limit. In South East Asian and South Chinese populations (see [[#International variations|§ international variations]]), BMI Prime should be calculated using an upper limit BMI of 23 in the denominator instead of 25. BMI Prime allows easy comparison between populations whose upper-limit optimal BMI values differ.<ref>{{cite journal | vauthors = Gadzik J | title = "How much should I weigh?"--Quetelet's equation, upper weight limits, and BMI prime | journal = Connecticut Medicine | volume = 70 | issue = 2 | pages = 81–88 | date = February 2006 | pmid = 16768059 }}</ref>

===Waist circumference===
{{Main|Waist-to-height ratio|Waist-to-hip ratio}}
Waist circumference is a good indicator of [[visceral fat]], which poses more health risks than fat elsewhere. According to the U.S. [[National Institutes of Health]] (NIH), waist circumference in excess of {{convert|102|cm}} for men and {{convert|88|cm}} for (non-pregnant) women, is considered to imply a high risk for type 2 diabetes, [[dyslipidemia]], hypertension, and CVD. Waist circumference can be a better indicator of obesity-related disease risk than BMI. For example, this is the case in populations of Asian descent and older people.<ref>{{cite web |url=http://www.nhlbi.nih.gov/health-pro/guidelines/current/obesity-guidelines/e_textbook/txgd/4142.htm |title=Obesity Education Initiative Electronic Textbook - Treatment Guidelines |website=US National Institutes of Health |date= |access-date=29 July 2016 |url-status=live |archive-url=https://web.archive.org/web/20170501084223/https://www.nhlbi.nih.gov/health-pro/guidelines/current/obesity-guidelines/e_textbook/txgd/4142.htm |archive-date=1 May 2017 |df= }}</ref> {{convert|94|cm}} for men and {{convert|80|cm}} for women has been stated to pose "higher risk", with the NIH figures "even higher".<ref>{{cite web|url=http://www.nhs.uk/chq/Pages/849.aspx?CategoryID=51|title=Why is my waist size important?|website=UK HNS Choices|date=|access-date=29 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160806210351/http://www.nhs.uk/chq/Pages/849.aspx?CategoryID=51|archive-date=6 August 2016|df=}}</ref>

Waist-to-hip circumference ratio has also been used, but has been found to be no better than waist circumference alone, and more complicated to measure.<ref>{{cite web|url=https://www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/abdominal-obesity/|title=Waist Size Matters|website=Harvard School of Public Health|date=2012-10-21|access-date=29 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160821092935/https://www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/abdominal-obesity/|archive-date=21 August 2016|df=}}</ref>

A related indicator is waist circumference divided by height. The values indicating increased risk are: greater than 0.5 for people under 40 years of age, 0.5 to 0.6 for people aged 40–50, and greater than 0.6 for people over 50 years of age.<ref>{{cite web |url=http://www.hospimedica.com/critical-care/articles/294746805/waist-height-ratio-better-than-bmi-for-gauging-mortality.html |title=Waist-Height Ratio Better Than BMI for Gauging Mortality |date=18 Jun 2013 |access-date=7 April 2016 |url-status=live |archive-url=https://web.archive.org/web/20160417064352/http://www.hospimedica.com/critical-care/articles/294746805/waist-height-ratio-better-than-bmi-for-gauging-mortality.html |archive-date=17 April 2016 |df= }}</ref>

=== Surface-based body shape index ===
The Surface-based Body Shape Index (SBSI) is far more rigorous and is based upon four key measurements: the [[body surface area]] (BSA), vertical trunk circumference (VTC), waist circumference (WC) and height (H). Data on 11,808 subjects from the National Health and Human Nutrition Examination Surveys (NHANES) 1999–2004, showed that SBSI outperformed BMI, waist circumference, and [[Body Shape Index|A Body Shape Index (ABSI)]], an alternative to BMI.<ref>{{Cite web|title = A New Potential Replacement for Body Mass Index {{!}} RealClearScience|url = http://www.realclearscience.com/journal_club/2015/12/30/a_new_potential_replacement_for_body_mass_index_109492.html|website = www.realclearscience.com|access-date = 2015-12-31|url-status=live|archive-url = https://web.archive.org/web/20160101113606/http://www.realclearscience.com/journal_club/2015/12/30/a_new_potential_replacement_for_body_mass_index_109492.html|archive-date = 2016-01-01|df = }}</ref><ref name="rahman2015">{{cite journal | vauthors = Rahman SA, Adjeroh D | title = Surface-Based Body Shape Index and Its Relationship with All-Cause Mortality | journal = PLOS One | volume = 10 | issue = 12 | pages = e0144639 | year = 2015 | pmid = 26709925 | pmc = 4692532 | doi = 10.1371/journal.pone.0144639 | df =  | bibcode = 2015PLoSO..1044639R }}</ref>

: <math>\mathrm{SBSI} = \frac{(\text{H}^{7/4})(\text{WC}^{5/6})}{\text{BSA VTC}}</math>

A simplified, dimensionless form of SBSI, known as SBSI<sup>*</sup>, has also been developed.<ref name="rahman2015" />

: <math>\mathrm{SBSI^\star} = \frac{(\text{H}^2)(\text{WC})}{\text{BSA VTC}}</math>

===Modified body mass index===
Within some medical contexts, such as [[familial amyloid polyneuropathy]], serum albumin is factored in to produce a modified body mass index (mBMI). The mBMI can be obtained by multiplying the BMI by [[human serum albumin|serum albumin]], in grams per litre.<ref>{{cite journal | vauthors = Tsuchiya A, Yazaki M, Kametani F, Takei Y, Ikeda S | title = Marked regression of abdominal fat amyloid in patients with familial amyloid polyneuropathy during long-term follow-up after liver transplantation | journal = Liver Transplantation | volume = 14 | issue = 4 | pages = 563–570 | date = April 2008 | pmid = 18383093 | doi = 10.1002/lt.21395 }}</ref>

== See also ==<!-- Please keep entries in alphabetical order & add a short description [[WP:SEEALSO]] -->
* [[Allometry]]
* [[Body fat percentage]] (BFP)
* [[Relative Fat Mass]] (RFM)
* [[Body water]]
* [[Corpulence index]]
* [[History of anthropometry]]
* [[List of countries by Body Mass Index (BMI)]]
* [[Obesity paradox]]
* [[Somatotype and constitutional psychology]]
<!-- please keep entries in alphabetical order -->

==Notes==
{{reflist|group=note}}

== References ==
{{Reflist|30em}}

== Further reading ==
* {{cite book |editor1-first=Linda A. |editor1-last=Ferrera | name-list-format = vanc |year=2006 |title=Focus on Body Mass Index And Health Research |publisher=Nova Science |location=New York |isbn=978-1-59454-963-2}}
* {{cite book |editor1-first=Thomas T. |editor1-last=Samaras | name-list-format = vanc |year=2007 |title=Human Body Size and the Laws of Scaling: Physiological, Performance, Growth, Longevity and Ecological Ramifications |publisher=Nova Science |location=New York |isbn=978-1-60021-408-0}}
* {{cite book |editor1-first=Melinda S. |editor1-last=Sothern |editor2-first=Stewart T. |editor2-last=Gordon |editor3-first=T. Kristian |editor3-last=von Almen | name-list-format = vanc |year=2006 |title=Handbook of Pediatric Obesity: Clinical Management |publisher=CRC Press |edition=Illustrated |isbn=978-1-4200-1911-7}}

== External links ==
{{wiktionary|body mass index}}
<!-- Please do not add more links to more calculators. If you feel a particular online calculator has specific merits, please propose the link on the talk page. -->
* U.S. National Center for Health Statistics:
** [https://www.cdc.gov/growthcharts/ BMI Growth Charts for children and young adults]
** [https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/english_bmi_calculator/bmi_calculator.html BMI calculator ages 20 and older]

{{Authority control}}

{{DEFAULTSORT:Body Mass Index}}
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[[Category:Classification of obesity]]
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