What your BMI number means
Body Mass Index is a quick screening figure that relates your weight to your height. It does not measure body fat directly, but for most people it gives a reasonable indication of whether their weight sits in a healthy range for their height. Health organisations worldwide use it as a first-pass check.
How to use the BMI calculator
Enter your weight in kilograms and your height in centimetres. The calculator returns your BMI and the category it falls into. It uses the standard metric formula, so there is no need to convert to pounds or feet.
The formula and categories
BMI = weight (kg) ÷ height (m)². Someone who is 70 kg and 1.75 m tall has a BMI of 70 ÷ 3.0625 ≈ 22.9. The World Health Organisation categories are: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, and 30 or above obese.
Important limitations
BMI cannot tell muscle from fat, so a very muscular athlete may register as "overweight" while being extremely fit. It also does not account for age, sex, ethnicity, or where fat is stored on the body — and waist circumference is often a better guide to health risk. Treat BMI as one useful data point among several, not a diagnosis. If you are concerned about your weight, a doctor can interpret it alongside your overall health.