How to calculate BMI and what the result means

Steps

1. Measure your weight in kilograms and your height in centimetres. Here: 70 kg and 175 cm.
2. Turn the height into metres: 175 cm is 1.75 m.
3. Multiply the height by itself: 1.75 × 1.75 = 3.0625.
4. Divide the weight by that: 70 ÷ 3.0625 = 22.9.
5. Compare with the WHO categories, or enter your numbers in the BMI calculator.

The WHO categories

Under 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight and 30 or more is obese. At 170 cm, 90 kg gives a BMI of 31.1 (obese), 50 kg gives 17.3 (underweight), and the healthy range is 53.5 to 72.0 kg. At 150 cm, 60 kg gives 26.7, which is overweight, and the healthy range is 41.6 to 56.0 kg.

The healthy range is worked backwards from the 18.5 and 24.9 limits, so it shows the weights that would put you in the normal category at your height.

What BMI does not show

BMI does not see muscle, bone or where fat sits on the body, so a muscular person can score high without carrying much fat. It also varies with age and sex. Some Asian health guidelines use lower cut-offs, with overweight starting near 23. Treat BMI as a screening number, not a diagnosis.

What to do with the result

If your BMI is outside the normal range, it is a reason to talk to a doctor or dietitian, not a reason for a crash diet. A waist measurement or a body fat estimate gives a second view. This page gives general information, not medical advice.