BMI Calculator
Metric or imperial — your BMI and WHO category, live as you type.
How this is calculated
BMI = weight (kg) ÷ height (m)²
Worked example: 70 kg at 175 cm → 70 ÷ 1.75² = 22.9, inside the WHO normal-weight band. The "normal-weight range" line in the result inverts the formula for your height (18.5–24.9 × height²), which is a more useful target than the abstract score.
WHO adult categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
This is a screening number, not medical advice — BMI can misread muscular and elderly bodies, and it does not apply in pregnancy or childhood. Talk to a health professional about what your number means for you.
Frequently asked questions
How is BMI calculated?
BMI = weight in kilograms ÷ height in meters squared. Someone 175cm and 70kg has BMI 70 ÷ 1.75² = 22.9. The imperial toggle converts pounds and feet/inches to metric first using the exact definitions (1 lb = 0.45359237 kg, 1 in = 2.54 cm), then applies the same formula.
What do the BMI categories mean?
This calculator uses the WHO adult bands: under 18.5 is classed underweight, 18.5–24.9 normal weight, 25–29.9 overweight, and 30+ obesity. They are population-level screening bands, not individual diagnoses.
Is BMI accurate for everyone?
No — that is its honest limitation. BMI cannot tell muscle from fat, so muscular people can read "overweight" while lean, and it is not designed for children, pregnancy, or the very elderly. Treat it as a quick screen; waist measurements and body-fat estimates add the missing picture.
Is my weight sent anywhere?
No. The calculation runs entirely in your browser — nothing you type here is transmitted, logged, or stored on any server.