Anthropometry and nutritionDiabetology
BMI calculator — body mass index and healthy weight
Enter your weight and height to see your BMI with the WHO category and the healthy weight range for your height. Add your waist to get the waist-to-height ratio.
Interpretation
BMI (body mass index) is weight in kilograms divided by height in metres squared. For adults, WHO uses these categories:
| Category (WHO) | BMI [kg/m²] |
|---|---|
| Severe thinness | < 16.0 |
| Moderate thinness | 16.0–16.99 |
| Mild thinness (underweight) | 17.0–18.49 |
| Healthy weight | 18.5–24.99 |
| Overweight | 25.0–29.99 |
| Obesity class I | 30.0–34.99 |
| Obesity class II | 35.0–39.99 |
| Obesity class III | ≥ 40.0 |
In people of Asian background the risk of diabetes and heart disease rises at a lower BMI; WHO suggests additional action points of 23 and 27.5 kg/m².
Waist-to-height
The waist-to-height ratio (WHtR) is waist circumference divided by height. It reflects visceral fat better than BMI alone. NICE uses:
- below 0.5 — healthy,
- 0.5–0.59 — increased central adiposity and health risk,
- 0.6 or more — high central adiposity, further increased risk.
A simple rule: keep your waist to less than half your height.
How we calculate
BMI = weight [kg] ÷ height² [m²]
The healthy weight range is the weight that gives a BMI of 18.5–24.9 at your height. BMI Prime is BMI divided by 25 (the upper limit of normal); a value above 1.0 means overweight. Imperial units: 1 lb = 0.4536 kg, 1 ft = 30.48 cm, 1 in = 2.54 cm.
Limitations
- BMI does not distinguish fat from muscle: it overestimates fatness in muscular people and may underestimate it in older people with low muscle mass.
- It is not used in pregnancy or in children (use growth charts for them).
- It does not show where fat is stored, which is why waist circumference is worth measuring.
Sources
- WHO. Obesity: preventing and managing the global epidemic. Report of a WHO Consultation. WHO Technical Report Series 894, 2000. iris.who.int
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet 2004;363:157–163. doi.org
- NICE guideline NG246. Overweight and obesity management (2025) — classification by BMI and waist-to-height ratio. www.nice.org.uk
Frequently asked questions
What is a healthy BMI?
Is BMI the same for women and men?
How do I calculate a child’s BMI?
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This calculator is for education and does not replace a doctor’s assessment. Always interpret the result together with the history and examination.