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BMI Calculator

Calculate your body mass index and see the WHO adult category.

For everyoneWeight & body compositionv2.0.1

Your measurements

years

Calculated on your device. Nothing is sent to a server.

Your result will appear here

Enter your measurements, then press Calculate.

Methodology

WHO adult BMI classification

BMI = weight (kg) ÷ height (m)²

BMI is weight in kilograms divided by the square of height in metres. Categories follow the WHO classification for adults: under 18.5, 18.5–24.9, 25–29.9, 30–34.9, 35–39.9 and 40 or more.

Who it is for
Adults aged 18 and over.
Version
2.0.1

How this calculator works

Where the formula comes from

  • The weight-for-height index behind BMI was described by Adolphe Quetelet in the 1830s; the name 'body mass index' was introduced by Ancel Keys in 1972.[1]
  • WHO adopted BMI cut-offs for classifying underweight, overweight and obesity in adults in its 2000 technical report.[2]

The inputs

  • BMI is weight in kilograms divided by the square of height in metres; the adult categories use the same thresholds for men and women.[2]

Versions and alternatives

  • A 2004 WHO expert consultation found that some Asian populations have increased metabolic risk at BMI values below the usual overweight threshold and proposed additional public-health action points of 23 and 27.5 kg/m², without a single cut-off for all Asian populations.[3]

Where accuracy falls (published evidence)

  • BMI does not measure body fat directly and does not show how fat is distributed, so it is limited for judging an individual's body composition.[4]
  • At the same BMI, older adults tend, on average, to have a higher percentage of body fat than younger adults, partly because lean mass decreases with age.[5]
  • Children and teenagers need age- and sex-specific BMI references rather than the adult categories.[2]

What guidelines say

  • The 2018 US Preventive Services Task Force recommends that clinicians offer or refer adults with a BMI of 30 or more to intensive, multicomponent behavioural interventions.[6]

Sources

  1. Eknoyan G. Adolphe Quetelet (1796–1874)—the average man and indices of obesity. Nephrol Dial Transplant. 2008;23(1):47–51. doi:10.1093/ndt/gfm517
  2. World Health Organization. Obesity: preventing and managing the global epidemic. Report of a WHO consultation. WHO Technical Report Series 894. Geneva: WHO; 2000. PMID 11234459
  3. WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157–163. doi:10.1016/S0140-6736(03)15268-3
  4. Batsis JA, Mackenzie TA, Bartels SJ, et al. A requiem for BMI in the clinical setting. Curr Opin Clin Nutr Metab Care. 2017;20(5):314–321. doi:10.1097/MCO.0000000000000395
  5. Micozzi MS, Harris TM. Age variations in the relation of body mass indices to estimates of body fat and muscle mass. Am J Phys Anthropol. 1990;81(3):375–379. doi:10.1002/ajpa.1330810307
  6. US Preventive Services Task Force. Behavioral weight loss interventions to prevent obesity-related morbidity and mortality in adults: US Preventive Services Task Force recommendation statement. JAMA. 2018;320(11):1163–1171. doi:10.1001/jama.2018.13022

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on

Worked example: how to calculate BMI

Inputs

Weight
70 kg
Height
170 cm
Age
35 years

Result

Body mass index
24.2 kg/m²
Healthy weight range — lower limit
53.5 kg (≈ 117.9 lb)
Healthy weight range — upper limit
72 kg (≈ 158.7 lb)

Healthy weight range

Calculation:

70 / 1.7² = 24.22

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

  • BMI does not distinguish muscle from fat, so it can be high in muscular people.
  • It does not show where fat is stored; waist measurements add information.
  • Not for children and teenagers (use BMI-for-age) or pregnancy.
  • Some Asian populations have higher metabolic risk at BMI values below the usual overweight threshold; suitable cut-offs vary by population.

References

  1. World Health Organization. Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894. Geneva: WHO; 2000. https://iris.who.int/handle/10665/42330
  2. WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157–163. doi:10.1016/S0140-6736(03)15268-3

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