BMI Calculator

Body Mass Index is the quickest way to check whether your weight sits in the healthy range for your height. This free BMI calculator works out your BMI from kilograms and centimetres — or pounds and feet/inches — shows your WHO category, and gives the healthy weight range for your height.

Your numbers stay on your device: everything is calculated in your browser, with nothing uploaded or stored. Health changes with age, so pair this with the Age Calculator, and use the Percentage Calculator to work out a weight change as a percentage of your starting weight.

The BMI formula

Body Mass Index is weight divided by height squared: BMI = weight (kg) ÷ height (m)². Worked example: 70 kg at 175 cm means height 1.75 m, so BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.86, in the normal range. In imperial units the same person is about 154 lb at 5 ft 9 in — the calculator converts pounds and feet/inches before applying the formula.

WHO weight categories

Note the exact boundaries: 24.9 is normal, while 25.0 is overweight — the calculator applies the cut-offs exactly.

Your healthy weight range

For any height there is a weight range that keeps BMI between 18.5 and 24.9: from 18.5 × height² to 24.9 × height². At 175 cm that is 56.7 kg to 76.3 kg. The calculator shows your range alongside your BMI — more useful than the number alone, since it shows how far you are from the range.

What BMI does not measure

BMI is a screening tool, not a diagnosis. It cannot tell muscle from fat, so a muscular athlete can score as overweight while carrying little body fat. It fits adults best: children need age-based growth charts, and pregnancy, old age and some medical conditions change how the number should be read. If your result surprises you, a doctor or dietitian can check body composition properly.