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Calculate your Body Mass Index in metric or imperial units and see which WHO category it falls into.
A BMI calculator is a tool that computes your Body Mass Index — a single number that expresses body weight relative to height. It's the screening value clinicians, insurers, and public-health researchers have used for decades as a quick proxy for whether a person's weight is in a healthy range for their height. This calculator accepts either metric (kilograms and centimeters) or imperial (pounds and feet/inches) inputs, computes the BMI with the standard formula, and classifies the result into the four World Health Organization adult categories: underweight, normal, overweight, and obese. BMI is a screening tool, not a diagnosis — it doesn't distinguish muscle from fat, and it doesn't apply the same way to every population. Everything runs in your browser; no measurements are sent to a server.
Tap Metric if you measure weight in kilograms and height in centimeters. Tap Imperial if you use pounds, feet, and inches.
Type your current weight. Use a scale reading taken at a consistent time of day (e.g., morning, post-bathroom) for a stable number.
Enter your height in centimeters, or in feet and inches. Measure without shoes, standing tall against a wall for the best accuracy.
Your BMI appears instantly along with the WHO adult category (underweight, normal, overweight, or obese). Nothing you enter is transmitted or stored.
Metric: BMI = weight(kg) ÷ height(m)² Imperial: BMI = 703 × weight(lb) ÷ height(in)² Adult WHO classification (same for men and women): BMI < 18.5 → Underweight 18.5 ≤ BMI < 25 → Normal 25 ≤ BMI < 30 → Overweight BMI ≥ 30 → Obese
Body Mass Index is defined as mass divided by the square of height. In metric, height is converted from centimeters to meters before squaring; in imperial the result is multiplied by 703 to match the metric scale so the same category thresholds apply. The four-band classification comes from the WHO's adult global cut-offs and is population-agnostic — it does not adjust for age, sex, ethnicity, or body composition. Clinicians often pair BMI with waist circumference, body-fat measurement, or ethnicity-specific thresholds (South Asian populations, for example, use lower cut-offs).
Reference: WHO — A healthy lifestyle (BMI)
| Weight & height | BMI |
|---|---|
70 kg, 175 cm | 22.9 — Normal Metric: 70 ÷ (1.75 × 1.75) = 22.86, comfortably in the normal range. |
154 lb, 5 ft 9 in | 22.7 — Normal Imperial: 703 × 154 ÷ (69 × 69) = 22.75 — the same person as above in different units. |
90 kg, 170 cm | 31.1 — Obese Borderline obese: just above the 30.0 threshold. A heavily muscled athlete at this ratio could still be metabolically healthy, which is why BMI is paired with other measures. |
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