BMI Calculator

Weight in kilograms divided by height in metres squared. Someone 175 cm weighing 70 kg has an index of 70 ÷ (1.75 × 1.75) = 22.9, inside the normal band.

Under 18.5 is underweight, 18.5 to under 25 is normal, 25 to under 30 is overweight, 30 to under 35 is obesity class I, 35 to under 40 is class II, and 40 or more is class III. Note that exactly 25 falls in overweight, not normal — a boundary calculators using "less than or equal" get wrong.

There is no single number. The index gives a range: every weight between an index of 18.5 and 24.9 is equally normal. So the tool shows the whole range for your height rather than inventing one figure the measure does not support.

No. It cannot tell what the weight is made of, so a muscular athlete can be classed overweight with low body fat, while someone with little muscle can look normal with high body fat. It is a population screening measure, not an individual diagnosis.

No. For children and teenagers under twenty, BMI is read against age- and sex-specific percentile charts rather than these fixed bands — the same number means something quite different.