How BMI is worked out
BMI = weight in kg ÷ (height in metres)². For example, 75 kg at 170 cm → 75 ÷ (1.70 × 1.70) = 26, which is overweight.
WHO categories for adults
| BMI | Category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obesity, class I |
| 35 – 39.9 | Obesity, class II |
| 40 and over | Obesity, class III |
The healthy weight for your height is the range that gives a BMI from 18.5 to 24.9.
Frequently asked questions
Is BMI accurate for everyone?
It's a quick general measure, but it can't tell muscle from fat. A very muscular athlete can show as overweight, and it reads differently for older people and during pregnancy.
Does it work for children?
No. For under-18s BMI is judged against age- and sex-specific growth charts, which a paediatrician uses.
What is the ideal weight for my height?
Enter your height and weight and the calculator shows the healthy weight range for your height, and how far you are from it.
For general information only. It doesn't replace advice from a doctor or dietitian.