BMI calculator
Your body mass index, the WHO category it falls into, the healthy weight range for your height — and the option to use the lower Asian cut-offs that apply in South and East Asia.
One formula, three numbers
BMI compares weight with height so that people of different sizes can be compared on one scale.
Measure without shoes
Measure height against a wall and weight on a level scale, ideally in the morning. A 2 cm error moves BMI by about 0.5; a 2 kg error moves it by about 0.7.
Divide weight by height²
BMI = kg ÷ m². At 170 cm and 65 kg: 65 ÷ (1.70 × 1.70) = 22.5. In imperial units, 703 × lb ÷ in² gives the identical number.
Read the range
18.5–24.9 is the international healthy band; 18.5–22.9 under the Asian standard. Anything outside is a prompt to look further, not a diagnosis.
What the numbers mean
Two standards, same measurement. Use the one your doctor or national health service uses.
| BMI | WHO international | WHO Asian |
|---|---|---|
| Below 18.5 | Underweight | Underweight |
| 18.5 – 22.9 | Healthy | Healthy |
| 23.0 – 24.9 | Healthy | Overweight |
| 25.0 – 27.4 | Overweight | Overweight |
| 27.5 – 29.9 | Overweight | Obese class I |
| 30.0 – 34.9 | Obese class I | Obese class I |
| 35.0 – 37.4 | Obese class II | Obese class II |
| 37.5 – 39.9 | Obese class II | Obese class III |
| 40.0 and above | Obese class III | Obese class III |
When BMI misleads
- Muscle. A rugby player and a sedentary person can share a BMI while carrying very different amounts of fat.
- Body shape. Fat around the waist carries more risk than fat on the hips. Waist-to-height ratio adds that information.
- Age. Adults over 65 often carry a little more weight safely; children need BMI-for-age percentile charts, not this scale.
- Ethnicity. That is exactly why the Asian cut-offs exist — the same BMI means different risk in different populations.
- Pregnancy. BMI is not meaningful during pregnancy; use your pre-pregnancy weight and medical advice.
Common questions
What is a healthy BMI?
Under the WHO international standard, 18.5 to 24.9. Under the WHO Asian standard, 18.5 to 22.9. Both are screening bands for adults — your doctor may set a different target based on blood pressure, blood sugar, waist measurement and family history.
How is BMI calculated?
Weight in kilograms divided by height in metres squared. In imperial units, 703 × weight in pounds ÷ height in inches squared. The calculator does both conversions for you and shows the same result in either unit system.
Which standard should I choose?
If you are of South Asian, Chinese, Japanese or other Asian descent, or you live in a country whose health service uses the lower cut-offs, choose WHO Asian. Otherwise use WHO international. The measurement is identical — only the category boundaries move.
How much weight should I lose or gain?
The healthy weight range shown is the weight that would put you between 18.5 and the upper limit for your height. Losing 5–10% of body weight already improves blood pressure and blood sugar for most people; plan changes with a clinician rather than aiming for a single number.
Is my data sent anywhere?
No. The calculation runs in your browser, like every tool on this site. Your height and weight are never uploaded or stored.