How BMI is calculated
BMI is your weight in kilograms divided by your height in metres, squared. For a person of 70 kg and 170 cm: 70 ÷ (1.70 × 1.70) = 24.2.
What the categories mean
For adults, the World Health Organization uses these ranges:
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 or more: obese
Where BMI falls short
BMI cannot tell muscle from fat, so a strong, muscular person can be labelled overweight. It also ignores where fat is carried on the body, age, and sex. Some groups have different risk levels at the same BMI.
What to look at alongside it
- Waist measurement
- Blood pressure and blood tests
- Fitness, energy and sleep
- Family history
When to talk to a professional
If your BMI is in the underweight or obese range, or you are worried about your weight, speak to a doctor or dietitian. This site gives general information and is not medical advice.