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The formula
BMI = weight (kg) ÷ height² (m²)
BMI = (weight (lb) ÷ height² (in²)) × 703
WHO categories
| Range | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Normal |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese class I |
| 35.0 – 39.9 | Obese class II |
| ≥ 40 | Obese class III |
Body Mass Index
A statistical measure proposed by Adolphe Quetelet in 1832 to compare body mass across populations of similar build.
Where BMI fails
Not a body-fat test
Muscular athletes routinely score 27+ (overweight) without excess fat. Conversely, an inactive person of 'normal' BMI may have unhealthy visceral fat.
Calculate yours
Use our calculator to compute BMI in metric or imperial — and see the WHO band you fall into.
Related converters
The tools mentioned in this guide — one tap away.
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