BMI Calculator
Body mass index from your height and weight, in metric or imperial units, with the standard WHO adult categories. Calculations run in your browser; nothing you enter is transmitted or stored.
Calculate your BMI
Example: 70 kg at 175 cm → BMI 22.9 (normal weight).
What BMI measures — and what it doesn't
BMI scales weight for height so that populations of different statures can be compared on one number: 70 kg at 175 cm gives kg ÷ m² = 22.9, in the normal-weight band. It is a useful screening statistic precisely because it needs only two measurements — and a limited one for the same reason, since it says nothing about how weight is composed or where it is carried.
Reading the number in context
Two people with identical BMIs can have very different health profiles. Muscle mass, bone density, age, sex, and fat distribution all matter; waist measurements and the body-fat estimate add complementary signals. Trends over months are more informative than any single reading.
Frequently asked questions
What formula does BMI use?
Weight in kilograms divided by height in metres squared: kg ÷ m². Imperial inputs are converted first, which is equivalent to the familiar 703 × lb ÷ in² form.
What are the standard categories?
For adults, WHO defines: under 18.5 underweight, 18.5–24.9 normal weight, 25–29.9 overweight, and 30 and above obesity. Different cut-offs apply to children and teens, for whom age-and-sex percentile charts are used instead.
Is BMI accurate for athletes?
Often not. BMI cannot distinguish muscle from fat, so muscular people can read "overweight" while carrying little fat, and the reverse can happen with low muscle mass. Waist measurements and body-fat estimates add useful context.
Should I act on my BMI number?
Treat it as one screening signal, not a diagnosis. Discuss weight, diet, or exercise changes with a qualified healthcare professional who can see your whole picture.
Not medical advice: this calculator provides general educational estimates from published population formulas. It cannot account for your individual health context and must not be used to diagnose or treat any condition — consult a qualified healthcare professional. Measurements are processed locally in your browser and never transmitted. See the methodology page.