BMI Calculator — WHO and Asian-Adjusted

Body Mass Index is the most widely used screening number for body size. It was popularised by the Belgian astronomer Adolphe Quetelet in the 1830s and adopted as a public-health tool by Ancel Keys in 1972. It is a ratio, not a measurement of body fat — but at population scale it tracks fat-mass closely enough to be useful for risk screening.

The formula is simple and the same in every country:

• Metric: BMI = weight (kg) / height (m)²
• Imperial: BMI = (weight (lb) / height (in)²) × 703

The factor 703 is published by the CDC and exists only to absorb the unit conversion (1 lb = 0.45359237 kg, 1 in = 0.0254 m). Both forms produce the same BMI to within floating-point precision, which is why this calculator shows a CDC cross-check below the main result.

Once BMI is computed, the calculator looks it up in one of two classification tables. The WHO standardbands — underweight (< 18.5), normal (18.5–24.9), overweight (25–29.9), and obese class I/II/III (30+) — apply to most non-Asian adults. The Asian-adjusted scale, proposed by the WHO Expert Consultation in The Lancet (2004), uses lower action points (23 for overweight and 27.5 for obese) because South and East Asian populations carry more body fat at any given BMI and develop cardiometabolic disease at lower weights. The American Diabetes Association now recommends BMI ≥ 23 as the diabetes-screening threshold for Asian Americans.

The healthy-weight range shown for your height is derived by inverting the formula: weight = BMI × height². For BMI 18.5 to 24.9 on the WHO scale (or 18.5 to 22.9 on the Asian scale), the calculator multiplies by your height in metres squared to give the kilogram range. The "distance to healthy range" figure simply subtracts your current weight from the nearest boundary.

BMI Prime (BMI / 25) and the Ponderal Index (kg / m³) are shown as supplementary metrics. Ponderal Index is more stable for very tall or very short people, where standard BMI distorts because height appears squared rather than cubed. BMI itself remains a screening number — not a diagnosis. Muscle mass, frame size, fat distribution, and ethnicity all change what the same BMI means clinically.

• WHO — Body Mass Index (Global Health Observatory)
• WHO Expert Consultation (2004) — Appropriate BMI for Asian populations, The Lancet 363:157–163
• CDC — Adult BMI Calculator and methodology (imperial factor 703)
• NIH NHLBI — Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults
• American Diabetes Association — Standards of Care in Diabetes (BMI ≥ 23 screening for Asian Americans)

Classification tables and formulas on this page were last cross-checked against the WHO, CDC, and ADA sources on 2026-05-11. The page is reviewed annually and whenever any of these bodies publish updated guidance.