BMI Calculator
Calculate your Body Mass Index (BMI) to determine if you are at a healthy weight for your height.
BMI Weight Chart
Your ideal weight range: 53.5 kg - 72.0 kg
BMI: what it measures and what it cannot
Body mass index was designed in the 1830s to describe populations, not individuals. It remains useful as a cheap screening signal, but it does not measure body fat, and treating it as a diagnosis is a misuse that its own creator warned against.
Formula
BMI = weight (kg) / height (m)^2
For pounds and inches: BMI = 703 x weight (lb) / height (in)^2. The constant 703 converts the units, it is not a correction factor.
Where the index came from
Adolphe Quetelet, a Belgian statistician, devised the ratio in 1832 while studying the distribution of human physical characteristics. He was explicit that it applied to populations and was not a measure of individual body composition.
The name "body mass index" was coined by Ancel Keys in 1972, who found it the best of several simple weight-for-height ratios for epidemiological work - while noting that it was inappropriate for individual diagnosis.
The height-squared denominator is a statistical convenience rather than a biological law. Body mass scales closer to height cubed in principle, but real human proportions fall between the two, which is why BMI systematically overstates for tall people and understates for short people.
Who the standard categories do not fit
BMI cannot distinguish muscle from fat, and it says nothing about where fat is distributed. Several groups are routinely misclassified.
- Muscular athletes are frequently classed as overweight or obese despite low body fat, because muscle is denser than fat.
- Older adults lose muscle and bone density, so a "normal" BMI can conceal a high fat percentage - sometimes called sarcopenic obesity.
- Children and adolescents need age and sex-specific percentile charts; adult categories do not apply below 20.
- Pregnancy makes the figure meaningless, and clinical guidance uses pre-pregnancy BMI instead.
- People of South Asian, Chinese, and some other Asian ancestries carry elevated cardiometabolic risk at lower BMI, which is why the WHO published lower action points for these populations.
Better measures for individual risk
If the question is health risk rather than population statistics, other cheap measurements outperform BMI.
Waist-to-height ratio is the strongest simple predictor of cardiometabolic risk in most studies. The guidance is to keep your waist to less than half your height, a rule that needs no chart and adjusts automatically for body size.
Waist circumference alone carries thresholds of roughly 94 cm for men and 80 cm for women in European populations, with lower cut-offs for South and East Asian populations. Body fat percentage via DEXA, bioimpedance, or skinfolds gives composition directly, though accuracy varies considerably by method.
Worked example
A person weighs 82 kg and is 1.78 m tall. BMI = 82 / (1.78^2) = 82 / 3.168 = 25.9, which falls just inside the overweight band.
Their waist measures 84 cm. Waist-to-height ratio is 84 / 178 = 0.47, below the 0.5 threshold, indicating low central adiposity risk.
The two measures disagree, and the second is the more informative one. This is a common pattern in people who carry appreciable muscle mass, and it is precisely why BMI alone is a screening prompt rather than a conclusion.
WHO BMI categories for adults
| Category | General population | Asian population action point |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Normal range | 18.5 - 24.9 | 18.5 - 22.9 |
| Overweight | 25.0 - 29.9 | 23.0 - 27.4 |
| Obese class I | 30.0 - 34.9 | 27.5 and above |
| Obese class II | 35.0 - 39.9 | - |
| Obese class III | 40.0 and above | - |
The Asian-population action points come from the WHO expert consultation published in The Lancet in 2004.
Frequently Asked Questions
Related calculators
References
- WHO - Body mass index fact sheet and classification
- WHO expert consultation - appropriate BMI for Asian populations (Lancet, 2004)
- NICE guideline NG246 - overweight and obesity management
Last reviewed: 2026-08-07. This page is informational. For legal, medical, tax, or financial decisions, confirm the result with a qualified professional.