BMI Calculator

The BMI Calculator works out your Body Mass Index - a single number that relates your weight to your height. Enter kilograms and centimetres, or pounds with feet and inches, and it returns your BMI to one decimal place, the World Health Organization category that number falls into, and the weight range that would put you in the normal band for your height.

Body Mass Index is defined as weight in kilograms divided by height in metres squared. It was designed as a quick, cheap way to screen large populations for weight-related health risk, which is exactly why it is useful and exactly why it has limits. BMI does not measure body fat directly and cannot tell muscle from fat, so a lean athlete and a sedentary person can share the same score. It is not validated for children, pregnant people, or the very muscular.

This calculator keeps the maths transparent. It shows the formula it used, converts imperial input to metric internally so both unit systems give the same answer, and reports the healthy weight range and how far you are from it. Every calculation runs in your browser - your weight and height are never sent anywhere, logged, or stored.

BMI is a screening figure rather than a diagnosis, and its limits are well documented. It uses only height and weight, so it cannot tell muscle from fat: a trained athlete often reads as overweight and a sedentary person with the same figure is in a different position entirely. It is also less reliable at the extremes of height, since the formula divides by height squared while bodies do not scale that way. The WHO thresholds shown here were derived largely from European populations, and several health bodies use lower cut-offs for people of South and East Asian descent. It does not apply to children or to pregnancy, both of which use different charts. Treat the number as a prompt to ask a clinician, not as an answer.