BMI Calculator
This bmi calculator works in metric or imperial units: enter your height and weight and it returns your body mass index, the WHO band it falls in, and the weight range that would put you in the healthy band at your height. Remember that BMI is a screening measure, not a diagnosis — it cannot tell muscle from fat.
Work out your BMI
BMI is a screening measure, not a diagnosis: it cannot tell muscle from fat. Discuss results outside the healthy range with a clinician. Not for children — they use age-and-sex percentile charts.
The formula, both systems
BMI is weight divided by height squared. In metric units that is kilograms divided by metres squared: a person 1.75 m tall weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial units it is pounds divided by inches squared, multiplied by 703: a person 5 ft 9 in (69 inches) weighing 154 lb has a BMI of 154 ÷ (69 × 69) × 703 = 22.7. The calculator above does both, and also inverts the formula to show the weight range for the healthy band at your height — for 1.75 m, that is 18.5 × 1.75² = 56.7 kg up to 24.9 × 1.75² = 76.3 kg.
WHO bands
The World Health Organization bands below apply to adults. They are population-level cut-offs, chosen because health risks rise across them on average — not personal verdicts.
| BMI | WHO band |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal (healthy) range |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
What BMI cannot see
BMI uses only height and weight, so it cannot distinguish a muscular build from a high body-fat one: athletes and manual workers often land in the overweight band with low body fat, while someone with low muscle mass can land in the healthy band with a high body-fat percentage. It also does not account for age, sex, pregnancy or where fat is carried — abdominal fat carries more risk than the same weight carried elsewhere — and the bands were developed largely from European populations, so some health services use lower cut-offs for South Asian adults. Waist circumference, waist-to-height ratio and a clinician's assessment all add information BMI alone cannot give.
Using the result sensibly
Treat the band as a prompt, not a prescription. A result outside the healthy range is worth discussing with a clinician, especially alongside blood pressure, cholesterol, blood sugar and family history; a result inside it is not a clean bill of health on its own. For children and teenagers, BMI is interpreted against age-and-sex percentile charts, not these adult bands, so do not use this calculator for them. And if you are tracking change over time, weigh under consistent conditions — same time of day, similar clothing — because a kilogram or two of daily variation moves the number more than most people expect.
bmi calculator questions
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Sources & official guidance
Screening information only, not medical advice — BMI cannot diagnose health; discuss results with a clinician. See our disclaimer.