BMI Calculator for Females and Males

How the BMI Calculator works

Body mass index is weight divided by height squared: kilograms over metres squared, or pounds over inches squared multiplied by 703. That is the entire formula. It takes two numbers and gives one, and everything people argue about follows from how little it can possibly know.

BMI calculator metric and imperial: worked examples

Metric: 70 kg at 175 cm is 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9, inside the healthy band. Imperial: 154 lb at 5'9" (69 inches) is 154 × 703 ÷ (69 × 69) = 108,262 ÷ 4,761 = 22.7 — the same person, with the small gap coming from rounding the unit conversions. The calculator accepts either set of units and does both calculations exactly.

Body mass index categories

The adult categories in general use come from the World Health Organization. These are population screening bands, not a diagnosis of anything.

Healthy weight range for my height

The calculator shows the weights that give a BMI of 18.5 to 24.9 at your exact height; the table gives the same range at common heights.

What does BMI actually measure?

It does not measure body fat. It measures mass, and it cannot tell which kind. Muscle is denser than fat, so a heavily built athlete and a sedentary person of the same height and weight get the same BMI and are in completely different physical condition. It does not know where fat sits, and fat around the abdomen carries different risk from fat on the hips and thighs — which is why waist circumference and waist-to-height ratio are often more informative on their own. It does not know your age, and body composition shifts with age at a constant weight. It does not know your sex, despite men and women carrying quite different proportions of fat at the same index.

The height problem

Dividing by height squared is a convenience, not a law. Human bodies scale closer to height cubed as volume, so the square in the denominator systematically pushes tall people up the scale and short people down. Adolphe Quetelet worked the ratio out in the 1830s while studying the statistical distribution of a population — he was not building a health measure, and he said so. The index only became a clinical shorthand in the 1970s, chosen largely because it was the least bad of the simple ratios available.

Cut-offs are not universal

Risk at a given BMI varies between populations, and the WHO identifies lower action points — around 23 rather than 25 — for many Asian populations, because the risk of type 2 diabetes and cardiovascular disease rises at a lower index. Standard adult categories also do not apply to children and adolescents, who are assessed on age-and-sex percentile charts, or to pregnant women.

Used as intended, BMI is a cheap first-pass screen across a population. It is a poor description of an individual, and it is not a health assessment. This calculator does the arithmetic and nothing more — for anything about your own health, talk to a doctor.

More BMI examples

The formula: BMI = weight in kg ÷ (height in m)².

First example. 85 kg at 180 cm is 85 ÷ 3.24 = 26.2, overweight. The healthy range at that height is 59.9 to 80.7 kg.

Second example. 55 kg at 168 cm is 55 ÷ 2.8224 = 19.5, inside the healthy band.

How many kilograms to a healthy BMI? Take 24.9 × height² from your weight: at 180 cm and 85 kg that is 85 − 80.7 = 4.3 kg.

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