BMI Calculator
Calculate your body mass index on the WHO adult scale, in metric or imperial units, and see the weight range that counts as normal for your height. A screening number, not a diagnosis — the limits are explained below.
What the number is good for
BMI earns its place as a fast, free screening measure: it needs a scale and a tape measure, and across large groups it correlates with health outcomes strongly enough that clinics and studies use it everywhere. The same simplicity is its limit — the formula sees mass, not what the mass is made of, where it sits, or who is carrying it.
Reading your result honestly
Two people with the same BMI can be in very different shape, and the borderline bands matter less than trends: a BMI drifting steadily upward over years says more than any single reading. The number is most useful alongside waist circumference, blood pressure and the other measurements a routine check-up collects — and any decision worth making from it is worth making with a clinician.
Everything on this page runs locally; nothing you enter is stored or sent anywhere.
Frequently asked questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. 70 kg at 1.75 m is 70 ÷ 1.75² ≈ 22.9. Imperial entries are converted first — height as feet plus inches, weight from pounds — and the classification always runs on the exact value, so a BMI displaying as 25.0 can still sit on either side of the overweight line depending on the unrounded figure.
What do the categories mean?
They are the WHO's adult screening bands: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese. They were built to compare populations, and at the population level they track health risk well. For any single person they are a starting point for a conversation with a doctor, not a verdict.
Why can BMI mislead for athletes and older adults?
Because it cannot tell muscle from fat. A muscular athlete can read overweight while carrying very little fat; an older adult who has lost muscle can read normal while carrying more fat than the number suggests. Waist circumference and body-composition measurements answer the question BMI cannot.
Does this scale apply to children?
No. For anyone under 20, BMI is interpreted through age-and-sex percentile charts, because a healthy value changes throughout growth — a number that is normal at 16 can be underweight at 6. Paediatric growth charts, not this adult scale, are the right tool there.
What is the normal-range weight shown next to the result?
Your height squared multiplied by the two edges of the normal band: 18.5 and 25. It is the span of weights that would land your BMI in the normal category — useful as a reference range, with the same caveats as the index itself.
Is my data stored or sent anywhere?
No. The calculation runs entirely in your browser and the fields are not saved — height and weight are exactly the kind of personal figures this site's design rule keeps off the disk. Reload the page and they are gone.
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