History
Who invented BMI and why: from Adolphe Quetelet's 1830s statistics to Ancel Keys' 1972 name, the 1998 cutoffs, waist-to-height ratio and the 2023-2025 rethink.
Key takeaways
- Adolphe Quetelet observed in the 1830s that adult weight is "nearly as the square of the stature"; he was describing populations, not diagnosing people.[1]
- Ancel Keys named the "body mass index" in 1972 after testing several indexes in 7,424 men in five countries.[5]
- The NIH set 25 (overweight) and 30 (obesity) in 1998 and called the cutoffs "somewhat arbitrary" because risk rises gradually.[9]
- Waist-to-height ratio outperformed BMI for spotting heart and metabolic risk in a meta-analysis of more than 300,000 adults.[13]
- Since 2023 the AMA, and since 2025 a Lancet Commission, advise using BMI together with other measures rather than alone.[15]
In short: BMI was invented by a Belgian astronomer and statistician, Adolphe Quetelet, who noticed in the 1830s that adult weight rises roughly with the square of height. It was a tool for describing the “average man,” not for judging anyone’s health. The name “body mass index” came much later, in 1972, from American physiologist Ancel Keys, and the familiar cutoffs of 25 and 30 were adopted by the NIH and the World Health Organization in the late 1990s. Since 2023, major medical groups have said BMI works best as a first screening number, used alongside waist size and other measures.
This page tells the story of how a 19th-century statistics project became the number on your chart, and why doctors are now adding measures beside it. If you just want your number, our BMI calculator works it out in seconds; for the wider story of weight and health, see our history of weight loss.
How BMI came to be, at a glance
- 1830sQuetelet finds that adult weight rises about with the square of height (described 1832, in his 1835 book).
- Before BMIDoctors use height-weight tables built from life-insurance data (revised as late as 1983).
- 1972Ancel Keys tests several weight indexes in 7,424 men and names the winner the "body mass index".
- 1985An NIH consensus conference reviews the health effects of obesity.
- 1997-1998A WHO consultation and new NIH guidelines set 25 for overweight and 30 for obesity.
- 2004WHO experts note higher risk at lower BMI in many Asian populations.
- 2022-2025Waist-to-height ratio joins BMI in UK guidance; the AMA and a Lancet Commission say BMI alone is not enough.
1830s: an astronomer counts people
Adolphe Quetelet (1796 to 1874) was a Belgian mathematician, astronomer and statistician who wanted to apply the tools of astronomy to human beings. He measured births, deaths, heights and weights to describe what he called the “average man.” According to a 2008 history in the journal Nephrology Dialysis Transplantation, he described the weight-height relationship in 1832, and it appeared in his principal work, Sur l’homme et le développement de ses facultés, published in 1835 and translated into English in 1842 as A Treatise on Man and the Development of His Faculties.
In the English edition, Quetelet explains that if people grew equally in every direction, weight would rise with the cube of height, but that is not what he saw. Between infancy and puberty, he wrote, weight increases nearly as the square of height, and when he compared fully grown adults of different heights, he found their weight was “nearly as the square of the stature.” That observation, weight divided by height squared, is the whole of the BMI formula.
Two things are worth knowing. First, Quetelet was describing averages in a population, not diagnosing anybody; his treatise is about statistics, growth and social patterns, not about obesity. Second, his ratio was known for over a century as the “Quetelet index.” He went on to organize the first International Statistical Congress in 1853, which pushed for a common list of causes of death, an early ancestor of today’s International Classification of Diseases.
Before BMI: insurance height-weight tables
For much of the 20th century, doctors did not use Quetelet’s ratio. They used height-weight tables. A 2000 review in Annals of Pharmacotherapy explains that these tables were built to compare groups by relative weight, and that because the weights in them were linked to lower death rates among insured people, they came to be called “desirable” or “ideal” weights. The search for a simpler index, the 2008 history adds, began after life-insurance actuaries reported higher death rates among their heavier policyholders.
The tables had quirks. The Metropolitan Life tables of 1983 split people into small, medium and large frames by elbow width, which was supposed to put about 25%, 50% and 25% of people in each group. When Canadian researchers tested this in 19,305 people in 1989, the split did not hold, and very few people came out as large-framed. The “ideal body weight” formulas used to dose some medicines, such as Devine’s equations, grew out of these same tables; the 2000 review found that the various formulas agree because the tables behind them agree. Our ideal weight calculator shows these formulas side by side and explains their limits.
1972: Ancel Keys gives it a name
After World War II, researchers studying heart disease needed a way to compare body weight across very different countries. Ancel Keys of the University of Minnesota, working with colleagues in Italy, Finland and Japan, tested several “indices of relative weight” in 7,424 healthy men in 12 groups across five countries, plus body-density measurements in two smaller groups. They judged each index by two tests: it should not depend much on height, and it should track body fat as closely as possible.
The ponderal index, which uses the cube root of weight, did worst. Percentage of average weight for height worked, but only within a given population. Weight divided by height squared came out slightly better than weight divided by height, and in their 1972 paper in the Journal of Chronic Diseases the authors wrote that “the ratio of weight to height squared, here termed the body mass index,” seemed preferable because it was simple to calculate and could be applied to all populations at all times. Note what they did and did not claim: BMI was the best of several simple options for comparing groups, not a precise measure of an individual’s fat.
The studies behind the number
- 7,424men in 12 groups across five countries in the 1972 study that named the body mass indexKeys A et al., J Chronic Dis 1972
- 97 millionU.S. adults estimated to be in the overweight or obesity range when the NIH set its 1998 cutoffsNHLBI Clinical Guidelines, 1998
- 40.3%of U.S. adults had obesity by BMI in August 2021 to August 2023CDC NCHS Data Brief 508, 2024
Checked on October 7, 2026
1985 to 1998: the cutoffs we use today
BMI moved from research into the clinic over the next quarter century. In February 1985, the National Institutes of Health held a consensus development conference on the health implications of obesity, published that December in Annals of Internal Medicine. In June 1997, a World Health Organization consultation in Geneva met on preventing and managing obesity; its report, Obesity: Preventing and Managing the Global Epidemic, followed in 1998 and was later issued in WHO’s Technical Report Series. WHO’s definitions today are simple: for adults, overweight is a BMI of 25 or more and obesity a BMI of 30 or more.
In September 1998, the NIH’s National Heart, Lung, and Blood Institute published its Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. It defined overweight as a BMI of 25 to 29.9 and obesity as 30 or above, estimated that 97 million American adults were in those ranges, and noted that a BMI of 30 equals about 221 pounds for someone 6 feet tall and 186 pounds at 5 feet 6. The guidelines also paired BMI with a second number: waist circumference above 40 inches for men or 35 inches for women signaled higher risk. The same report admitted that the cutoffs are “somewhat arbitrary,” because disease risk rises gradually as weight rises rather than jumping at one number.
Those data also show how quickly things changed. Using the new definitions, national surveys found that obesity rose from 10.4% to 19.9% of men and from 15.1% to 24.9% of women between 1960 and 1994. By August 2021 to August 2023, the CDC found that 40.3% of American adults had a BMI of 30 or more, and 9.4% had severe obesity (a BMI of 40 or more).
| Item | Men | Women |
|---|---|---|
| 1960 | 10.4% | 15.1% |
| 1994 | 19.9% | 24.9% |
Obesity = BMI of 30 or more. By 2021-2023 the CDC put the figure at 40.3% of all adults (men and women together).
Source: NHLBI Clinical Guidelines on Overweight and Obesity in Adults (1998), citing NCHS/CDC surveys (checked on October 7, 2026)
The categories, as used today
The CDC’s adult categories, for ages 20 and up, are below. The CDC calls BMI a screening measure and says it should be considered with other factors when assessing a person’s health; it is not a diagnosis.
| BMI | CDC category (adults 20+) | Lower thresholds NICE uses for some groups* |
|---|---|---|
| Below 18.5 | Underweight | Same |
| 18.5 to under 25 | Healthy weight | 18.5 to under 23 |
| 25 to under 30 | Overweight | 23 to 27.4 |
| 30 to under 35 | Obesity, class 1 | Obesity from 27.5 |
| 35 to under 40 | Obesity, class 2 | Classes 2 and 3 about 2.5 points lower |
| 40 or more | Obesity, class 3 (severe) |
2004: one number does not fit every body
Keys had hoped BMI would apply to all populations, but doubts appeared quickly. In 2004, a WHO expert consultation published in The Lancet reviewed evidence that many Asian populations have more body fat and higher health risks at the same BMI than European populations. It found that the BMI at which risk rises varies from 22 to 25 in different Asian populations, kept the international cutoffs, and suggested extra “public health action points” at 23, 27.5, 32.5 and 37.5. England’s NICE now uses lower thresholds for several groups, as shown in the table above.
There are other blind spots. The 2025 Lancet Commission described below notes that BMI can both underestimate and overestimate body fat: because it only sees weight, a very muscular person can score high, while someone who has lost muscle can score in the “healthy” range and still carry a lot of fat around the organs. That kind of deep belly fat, called visceral fat, matters for heart and metabolic health; our visceral fat guide explains why, and the belly fat guide covers what helps.
2012 to 2022: the waist joins the conversation
Because BMI can’t see where fat sits, researchers looked for a simple measure that can. A 2012 meta-analysis in Obesity Reviews pooled 31 studies covering more than 300,000 adults in several ethnic groups and found that waist-to-height ratio was better than both waist size and BMI at picking out people with high blood pressure, diabetes and other heart and metabolic risk factors. Waist size alone improved on BMI by about 3%, and waist-to-height ratio by about 4% to 5%.
In 2022, England’s National Institute for Health and Care Excellence (NICE) added waist-to-height ratio to its guidance for adults with a BMI under 35, with a memorable message: keep your waist to less than half your height. Its current guideline sorts a ratio of 0.4 to 0.49 as healthy, 0.5 to 0.59 as increased risk and 0.6 or more as high risk. You need only a tape measure: measure around your waist and divide by your height in the same units.
| BMI | Waist-to-height ratio | |
|---|---|---|
| What it is | Weight (kg) divided by height (m) squared | Waist divided by height, same units |
| Where it came from | Quetelet (1830s); named by Keys (1972) | Backed by a 2012 meta-analysis; added to NICE guidance in 2022 |
| What it sees | Total weight for height | Fat around the middle (central adiposity) |
| Common cutoffs | 25 overweight, 30 obesity (lower for some groups) | Under 0.5 healthy; 0.5 to 0.59 increased; 0.6+ high |
| Main blind spot | Can’t tell muscle from fat or see where fat sits | Needs a careful tape measurement; NICE uses it for adults with a BMI under 35 |
| Best use | Population tracking and first screening | Adding a risk signal alongside BMI |
2023 to 2025: “useful, but not on its own”
In June 2023, the American Medical Association adopted a policy calling BMI an imperfect way to measure body fat. The policy notes that BMI was based mainly on data from earlier generations of non-Hispanic white people, that it has been used in ways that caused historical harm, and that it loses predictive power at the individual level. The AMA now suggests using BMI together with other measures such as waist circumference, body composition, visceral fat and metabolic factors, and says BMI alone should not be the reason to deny insurance coverage.
In January 2025, a Lancet Diabetes and Endocrinology Commission of 58 experts, including people with lived experience of obesity, went further. It recommended using BMI only as a population-level or screening measure, confirming excess body fat with a direct measurement or at least one other body measure such as waist circumference, waist-to-hip or waist-to-height ratio. It also proposed separating “preclinical obesity” (excess fat with normal organ function) from “clinical obesity” (excess fat that is already affecting how organs or daily activities work). For people with a BMI above 40, it said, excess fat can be assumed.
What this history means for your number
Almost two centuries on, Quetelet’s ratio is still the quickest way to sort large groups and to start a conversation, and many guidelines still use it. FDA labels for weight-management medicines, for example, describe their approved use in terms of BMI, as our FDA-approved medications comparison shows, and bariatric surgery criteria also start from BMI. But the history is clear that it was never meant to be the whole story about one person’s health. A gentler, more complete picture adds your waist, how you feel and function, and your blood pressure, blood sugar and cholesterol.
If you want more than one number, our body fat calculator estimates body fat from tape measurements, and our comparison of smart scales, DEXA and tape measures explains how accurate each method is. If you track at home, our best smart scales list explains what their body-fat readings can and can’t tell you, and if you are building muscle while losing fat, the body recomposition guide explains why the scale can stall while your shape changes. For how weight got counted in calories, read the companion story, the history of calorie counting.
Related guides
Shapewear vs Compression Garments vs Waist TrainersShapewear, compression garments and waist trainers compared: what each does and doesn't do, compression levels in…
Weight-Loss Meal Plan: A 7-Day Plan at 1,500 and 1,800 CaloriesA free 7-day weight-loss meal plan at 1,500 and 1,800 calories, with grams and calories for…
Alternate-Day Fasting vs 16:8 vs 5:2: Fasting Methods ComparedTypes of intermittent fasting compared: 16:8, 5:2 and alternate-day fasting, what a week looks like on…
GLP-1 Medication vs a Diet Program: Results, Costs and Trade-offsGLP-1 medication vs a diet program compared: average weight loss in STEP, SURMOUNT, Look AHEAD and…Questions to ask a professional
- What does my BMI mean alongside my waist size and blood tests?
- Do lower BMI thresholds apply to me because of my family background?
- Would a body-composition measurement be useful in my case?
- Which numbers should I track over time, and how often?
Frequently asked questions
Who invented BMI?
Belgian statistician and astronomer Adolphe Quetelet described the weight-to-height-squared relationship in the 1830s (it appears in his 1835 book). Ancel Keys gave it the name "body mass index" in 1972.
Was BMI designed to measure individual health?
No. Quetelet used it to describe the average proportions of a population, and Keys chose it as the best simple index for comparing groups. Today the CDC calls it a screening measure, not a diagnosis.
When did a BMI of 25 become "overweight"?
A WHO consultation in 1997 (report published 1998) and the NIH's September 1998 clinical guidelines used 25 to 29.9 for overweight and 30 or more for obesity, which are still the standard adult cutoffs.
Why do some groups use lower BMI cutoffs?
Many Asian populations, and several other groups, have more body fat and higher heart and metabolic risk at the same BMI. A 2004 WHO consultation suggested extra action points at 23 and 27.5, and NICE in England uses 23 and 27.5 for several groups.
Is waist-to-height ratio better than BMI?
It adds information BMI misses. A 2012 meta-analysis found it better at spotting cardiometabolic risk, and NICE advises keeping your waist to less than half your height. Most guidelines use it alongside BMI, not instead of it.
References
- Quetelet A.. A Treatise on Man and the Development of His Faculties (Edinburgh: W. and R. Chambers, 1842; English edition of Sur l’homme, 1835). Internet Archive (public-domain scan), 1842. (accessed October 7, 2026) Other
- Eknoyan G.. Adolphe Quetelet (1796-1874): the average man and indices of obesity. Nephrology Dialysis Transplantation, 2008. doi:10.1093/ndt/gfm517 · PMID 17890752 (accessed October 7, 2026) Review
- Pai MP, Paloucek FP. The origin of the “ideal” body weight equations. Annals of Pharmacotherapy, 2000. doi:10.1345/aph.19381 · PMID 10981254 (accessed October 7, 2026) Review
- Faulkner RA, Bailey DA. Critical evaluation of frame size determination in the 1983 Metropolitan Life weight for height tables. Canadian Journal of Public Health, 1989. PMID 2804868 (accessed October 7, 2026) Other
- Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. Indices of relative weight and obesity. Journal of Chronic Diseases, 1972. doi:10.1016/0021-9681(72)90027-6 · PMID 4650929 (accessed October 7, 2026) Other
- Health implications of obesity. National Institutes of Health Consensus Development Conference Statement (11-13 February 1985). Annals of Internal Medicine; National Institutes of Health, 1985. PMID 4062128 (accessed October 7, 2026) Government page
- Obesity: preventing and managing the global epidemic. Report of a WHO Consultation on Obesity, Geneva, 3-5 June 1997 (c1998), NLM Catalog record 9807275. World Health Organization; National Library of Medicine catalog, 1998. (accessed October 7, 2026) Government page
- Obesity and overweight (fact sheet). World Health Organization. (accessed October 7, 2026) Government page
- Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report (September 1998). National Heart, Lung, and Blood Institute (NIH), 1998. PMID 9813653 (accessed October 7, 2026) Guideline
- Obesity and Severe Obesity Prevalence in Adults: United States, August 2021-August 2023 (NCHS Data Brief 508). Centers for Disease Control and Prevention, National Center for Health Statistics, 2024. (accessed October 7, 2026) Government page
- Adult BMI Categories. Centers for Disease Control and Prevention. (accessed October 7, 2026) Government page
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet, 2004. doi:10.1016/S0140-6736(03)15268-3 · PMID 14726171 (accessed October 7, 2026) Guideline
- Ashwell M, Gunn P, Gibson S. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: systematic review and meta-analysis. Obesity Reviews, 2012. doi:10.1111/j.1467-789X.2011.00952.x · PMID 22106927 (accessed October 7, 2026) Meta-analysis
- Overweight and obesity management (NG246): identifying and assessing overweight, obesity and central adiposity. National Institute for Health and Care Excellence (NICE), 2025. (accessed October 7, 2026) Guideline
- AMA adopts new policy clarifying role of BMI as a measure in medicine. American Medical Association, 2023. (accessed October 7, 2026) Society statement
- Rubino F, Cummings DE, Eckel RH, et al.. Definition and diagnostic criteria of clinical obesity. Lancet Diabetes & Endocrinology, 2025. doi:10.1016/S2213-8587(24)00316-4 · PMID 39824205 (accessed October 7, 2026) Guideline
Facts checked on October 7, 2026
Educational information, not medical advice. Talk with a qualified healthcare professional about your own situation. In an emergency call 911.
Leave a Reply