// health › Body Composition
Body Mass Index from weight and height, with the WHO weight-status band it falls in.
BMI = weight (kg) / [height (m)]²
Body Mass Index is a single number that compares your weight to your height. It divides your weight in kilograms by the square of your height in metres. It is a quick screening figure, not a diagnosis — it tells you roughly which weight band you sit in, which can be a starting point for a conversation with a doctor.
The World Health Organization splits BMI into four ranges for adults: below 18.5 is underweight, 18.5 to just under 25 is the normal range, 25 to just under 30 is overweight, and 30 and above is obese. The cut-offs are the same for men and women.
The bar is split into the four coloured bands in order, from underweight on the left to obese on the right. The needle drops onto the bar at your calculated score, so you can see at a glance which band you land in and how close you are to the next boundary.
BMI only knows your weight and height — it cannot tell muscle from fat. A very muscular athlete can read as overweight while carrying little fat, and BMI is less reliable for older adults, pregnant people, and children, who use age-and-sex percentile charts instead. Treat it as one rough signal among several, never the whole picture.
BMI is used as a fast screening tool. A clinic might record it at a check-up: someone 70 kg at 1.75 m has a BMI of about 22.9, squarely in the normal range. An insurer or a population health study might use it to flag groups for follow-up. In each case it is a first filter that points to whether a closer look is worth taking.