Body Mass Index is a quick screen that compares your weight to your height. It does not measure body fat directly, but it is a useful starting point that doctors and health bodies use to flag whether a weight is in a healthy range.

How it is calculated

BMI is your weight in kilograms divided by your height in metres squared. Switch to imperial and the calculator converts pounds and inches for you, so the result is the same either way.

The standard ranges

Under 18.5 — underweight
18.5 to 24.9 — healthy weight
25 to 29.9 — overweight
30 and above — obese

Where BMI falls short

BMI does not tell muscle from fat, so very athletic people can read high while being lean. It also varies with age and ethnicity. Treat it as one signal, not a verdict.

For general information, not medical advice. Talk to a clinician about your health.