How to Calculate BMI by Hand

BMI takes ten seconds with the right formula. Here's how it works — then verify with the calculator.

The BMI formula (metric)

BMI = weight in kilograms ÷ (height in meters)². Example: 70 kg, 1.75 m → 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9 — healthy range.

The imperial version

BMI = 703 × weight(lb) ÷ (height(in))². Example: 154 lb, 69 in → 703 × 154 ÷ 4761 = 22.7.

Reading the result

Below 18.5: underweight. 18.5–24.9: healthy. 25–29.9: overweight. 30+: obesity. These are WHO screening cutoffs.

What BMI doesn't tell you

Muscle vs fat, fat distribution, fitness, or health history. Athletes often score 'overweight' while lean — use BMI as one signal, not a verdict.

Check yours instantly

Skip the arithmetic: our free BMI calculator handles both unit systems and categorizes your result.