BMI Calculator
Body mass index for adults in metric or US units, with the WHO categories.
How to use BMI Calculator
- Choose metric or US units.
- Enter weight and height.
- Read your BMI, its WHO category and the healthy weight range for your height.
How it works
BMI = weight (kg) ÷ height (m)², or 703 × weight (lb) ÷ height (in)². The World Health Organization classifies adult BMI as underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9 and obesity from 30 (class I 30–34.9, class II 35–39.9, class III 40 and above).
BMI is a quick screening number, not a diagnosis. It does not distinguish muscle from fat, so athletes can score "overweight", and it does not show where fat is stored. A WHO expert consultation noted that many Asian populations have higher health risks at lower BMI values. It does not apply to children and teenagers, whose BMI must be compared with age- and sex-specific growth charts. Talk to a health professional about your own situation.
Example
72 kg at 1.75 m: 72 ÷ 1.75² = 23.5 (healthy weight). The healthy range for 1.75 m is about 56.7–76.3 kg.
Frequently asked questions
Is BMI accurate?
It is a useful population-level screening tool but imprecise for individuals: it ignores muscle mass, bone density and fat distribution. Waist measurement adds useful information.
Can I use it for my child?
No. Children and teenagers need BMI-for-age percentiles from growth charts (such as the WHO or CDC charts), which this calculator does not provide.
Does BMI differ for men and women?
The adult formula and WHO cut-offs are the same for both sexes, although body composition differs.
What is BMI Prime?
BMI divided by 25, the upper limit of the healthy range. A value above 1.0 means above the healthy range.
Limitations
- Adults (18+) only.
- Not suitable during pregnancy.
- Not medical advice; consult a healthcare professional.
Last reviewed November 9, 2026. How we build and test tools.