How to calculate Body Mass Index BMI (EN): the BMI is the universal anthropometric indicator adopted by the World Health Organization WHO Geneva for adult weight status assessment. Reference frameworks: NIH National Institutes of Health Bethesda Maryland, CDC Centers for Disease Control Atlanta Georgia, NHANES National Health and Nutrition Examination Survey, USDA US Department of Agriculture Dietary Guidelines for Americans, FDA Food and Drug Administration, NHS National Health Service UK, Public Health England Better Health, Health Canada, Australian Government Department of Health Healthy Weight Guide. Specialty societies: The Obesity Society TOS Bethesda, American Heart Association AHA Dallas, American College of Cardiology ACC, American Diabetes Association ADA Arlington, American Society for Metabolic and Bariatric Surgery ASMBS, British Obesity Society, European Association for the Study of Obesity EASO, World Obesity Federation London.

Clinical centers: Mayo Clinic Rochester, Cleveland Clinic, Johns Hopkins Baltimore, Mass General Brigham Boston, Mount Sinai New York, Stanford Health Care, UCSF San Francisco, NIH Clinical Center, Joslin Diabetes Center Boston. Pharma anti-obesity: Novo Nordisk semaglutide Ozempic Wegovy, Eli Lilly Indianapolis tirzepatide Mounjaro Zepbound, Pfizer, AbbVie, Amgen, Currax Pharmaceuticals Contrave. Fitness industry: Peloton New York, Nautilus Vancouver Washington, Life Fitness Rosemont Illinois, Cybex International, Bowflex, Tonal San Francisco, Mirror by Lululemon, Hydrow. The BMI = weight(kg) / height(m)^2 formula was defined by Belgian astronomer-statistician Adolphe Quetelet in 1832 (Quetelet Index) and renamed Body Mass Index by US epidemiologist Ancel Keys University of Minnesota in his landmark Indices of relative weight and obesity Journal of Chronic Diseases 1972. Keys is famous for the Seven Countries Study 1958-1970 origin of the Mediterranean diet concept.

WHO formalized BMI cutoffs in WHO Technical Report Series 854 1995 and refined them in TRS 894 2000.

BMI Quetelet 1832 formula and WHO classification

Formula BMI = weight (kg) / height (m)^2. Example male 75 kg height 1.75 m: BMI = 75/(1.75^2) = 75/3.0625 = 24.5 kg/m^2 (upper-normal weight). Convert height cm to m: 175 cm = 1.75 m (divide by 100). Convert lb to kg and in to cm: 1 lb = 0.4536 kg, 1 in = 2.54 cm; e.g. 165 lb = 74.84 kg, 5 ft 9 in = 175.3 cm. Ideal weight range: min = 18.5 * height^2; max = 24.9 * height^2. For 1.75 m: min = 56.7 kg (125 lb); max = 76.3 kg (168.2 lb). WHO classification: BMI <16 severe underweight (anorexia, cachexia, malnutrition risk), 16-18.49 underweight (amenorrhea, early osteoporosis, immunodeficiency risk), 18.5-24.9 normal weight (lowest cardio-metabolic risk), 25-29.9 overweight (pre-obesity), 30-34.9 obesity class I (moderate comorbidity risk), 35-39.9 obesity class II (high risk), ≥40 obesity class III or morbid (very high risk, bariatric surgery indication per ASMBS guidelines). Limitations: BMI does not differentiate lean from fat mass; underestimates fat mass in sarcopenic elderly; overestimates risk in muscular athletes; does not account for visceral fat distribution.

History BMI from Quetelet 1832 to WHO 2000

The Quetelet Index was proposed in 1832 by Belgian astronomer-mathematician-statistician Lambert Adolphe Jacques Quetelet (1796-1874) University of Ghent, founder of social physics and modern anthropometry; pioneer of applied statistics; magnum opus Sur l'homme et le developpement de ses facultes ou Essai de physique sociale 1835 (English translation A Treatise on Man). The current term Body Mass Index BMI was introduced by US epidemiologist Ancel Keys University of Minnesota Minneapolis in the seminal Indices of relative weight and obesity Journal of Chronic Diseases 25(6-7):329-343 1972 where he validated the superiority of weight/height^2 over alternatives (Broca, Lorentz, Pignet, ponderal). Keys is renowned for the Seven Countries Study 1958-1970 (Italy, Greece, Yugoslavia, Netherlands, Finland, USA, Japan) origin of the Mediterranean diet concept; Italian cohorts at Crevalcore Bologna, Montegiorgio Fermo, Cilento Pioppi (Keys retired in Pioppi where he died at 100). The WHO World Health Organization Geneva adopted the BMI classification in WHO Technical Report Series 854 1995 Physical Status: The Use and Interpretation of Anthropometry and refined it in TRS 894 2000 Obesity: Preventing and Managing the Global Epidemic;

Asian cutoffs published in WHO Expert Consultation Lancet 363:157 2004 (BMI ≥23 overweight, ≥27.5 obesity for Asian populations). In the US the NIH NHLBI Clinical Guidelines on Identification, Evaluation and Treatment of Overweight and Obesity in Adults 1998 adopted WHO cutoffs; the USPSTF US Preventive Services Task Force recommends intensive behavioral intervention for adults with BMI ≥30. The UK NHS NICE guidance CG189 2014 confirms WHO classification.

WHO BMI Classification Table

5 numerical BMI examples

Example 1 woman 60 kg height 165 cm: height_m = 1.65; BMI = 60/(1.65^2) = 60/2.7225 = 22.04 kg/m^2 -> normal weight; ideal range 50.4-67.8 kg.

Example 2 man 95 kg height 178 cm: height_m = 1.78; BMI = 95/3.1684 = 29.99 -> borderline overweight/obesity; ideal 58.6-78.9 kg. Recommendation: -16 kg target via -500 kcal/day deficit + 150 min/week aerobic activity per AHA-ACSM-CDC Physical Activity Guidelines for Americans.

Example 3 athlete 90 kg height 175 cm: BMI = 29.39 -> nominally overweight but in a rugby player or NFL lineman with body fat <15% the BMI overestimates risk (athlete paradox); supplement with skinfold Durnin-Womersley, BIA bioimpedance or DEXA dual-energy X-ray absorptiometry.

Example 4 elderly 50 kg height 155 cm: BMI = 20.81 -> normal; however over age 65 the optimal range shifts to BMI 23-29.9 (elderly paradox protection from sarcopenia and frailty); add SARC-F screening EWGSOP2 sarcopenia and grip strength dynamometer.

Example 5 morbid obesity 140 kg height 168 cm: BMI = 49.6 -> obesity class III; multidisciplinary evaluation for bariatric surgery (sleeve gastrectomy, Roux-en-Y gastric bypass, mini gastric bypass, BPD/DS) per ASMBS American Society Metabolic and Bariatric Surgery 2022 guidelines.

BMI model limitations

BMI does not distinguish lean from fat mass: muscular athletes can have BMI >25 with low body fat (8-12%). BMI underestimates fat in sarcopenic elderly and chronic muscle-loss patients (HIV, oncology, COPD, heart failure). BMI does not capture fat distribution: waist circumference and waist-to-hip ratio (WHR) and waist-to-height ratio (WHtR) are stronger cardio-metabolic predictors (NCEP ATP-III/IDF cutoffs men >102 cm/0.90, women >88 cm/0.85). For Asian populations WHO cutoffs are lowered (BMI >23 overweight, >27.5 obesity) due to higher visceral adiposity at given BMI. In pregnancy pre-pregnancy BMI guides recommended weight gain per IOM 2009: underweight +12.5-18 kg, normal +11.5-16, overweight +7-11.5, obese +5-9. Under 18 use age-sex BMI percentiles (CDC 2-20 yr growth charts, WHO 0-5 and 5-19). Recommended adjuncts per AACE/TOS 2022 obesity guidelines: skinfold thickness, BIA, DEXA, abdominal MRI for visceral adipose tissue VAT.

Common errors

Common pitfalls: entering height in cm without converting to m (BMI = 75/175 = 0.43 wrong vs 24.5 correct); using lb and in without conversion (1 lb = 0.4536 kg, 1 in = 2.54 cm); applying BMI to children without age-sex percentiles; evaluating BMI in dialysis/edema/ascites where weight is distorted by fluid overload; over-interpreting BMI in bodybuilders ignoring body composition; ignoring sarcopenia in elderly; using BMI alone in oncology or chronic malnutrition. Confusing BMI with Body Adiposity Index BAI (Bergman 2011) or Sheldon somatotypes. Neglecting waist circumference NCEP ATP-III/IDF threshold for metabolic syndrome. Not reassessing BMI during rapid weight loss (>1 kg/week) which predisposes to yo-yo effect and lean mass loss.

BMI applications USA UK Worldwide

1. National surveillance: NHANES National Health and Nutrition Examination Survey CDC Atlanta NCHS, BRFSS Behavioral Risk Factor Surveillance, YRBSS Youth Risk Behavior, NHIS National Health Interview Survey, UK Health Survey for England HSE, Scottish Health Survey.
2. Clinical centers: Mayo Clinic Rochester Minnesota, Cleveland Clinic Bariatric Endocrinology Institute, Johns Hopkins Bayview Center for Obesity, Mass General Brigham Weight Center Boston, Joslin Diabetes Boston, NIH Clinical Center Bethesda, Vanderbilt Surgical Weight Loss.
3. Specialty societies: TOS The Obesity Society Bethesda, ASMBS American Society Metabolic and Bariatric Surgery Newberry Florida, AHA Dallas, ACC ADA AACE Endocrine Society, EASO European Association for Study of Obesity, World Obesity Federation London.
4. Anti-obesity pharma: Novo Nordisk Bagsvaerd Denmark (Ozempic Wegovy semaglutide), Eli Lilly Indianapolis (Mounjaro Zepbound tirzepatide), Pfizer (danuglipron), AbbVie, Amgen (MariTide), Currax (Contrave naltrexone-bupropion), Vivus (Qsymia), Rhythm (setmelanotide).
5. Fitness industry: Peloton New York, Nautilus Vancouver Washington, Life Fitness Rosemont Illinois, Cybex International, Bowflex, Tonal San Francisco, Mirror by Lululemon, Hydrow, Apple Fitness Plus, Garmin, Fitbit by Google, Whoop Boston, Oura Ring Finland.

Updated July 2026