How to check your BMI
- Choose metric (cm and kg) or imperial (feet, inches and pounds).
- Enter your height and weight. The result updates as you type.
- Read your BMI and its WHO category, then the South Asian and Indian readings below it.
- Check the healthy weight range for your height.
The BMI formula
BMI = weight (kg) ÷ height (m)²
For 70 kg at 1.70 m: 1.70 × 1.70 = 2.89, and 70 ÷ 2.89 = 24.2. In imperial units the calculator converts pounds and inches exactly; the shortcut 703 × pounds ÷ inches² gives the same answer to two decimals. BMI is shown to one decimal, as WHO and the NHS do, and the category is read from that figure, so 24.96 shows as 25.0 and counts as overweight.
BMI categories for adults
| Category | WHO | South Asian (NICE) | Indian consensus (2009) |
|---|---|---|---|
| Underweight | Under 18.5 | Under 18.5 | Under 18.0 |
| Healthy (normal) | 18.5–24.9 | 18.5–22.9 | 18.0–22.9 |
| Overweight | 25.0–29.9 | 23.0–27.4 | 23.0–24.9 |
| Obesity | 30 and over | 27.5 and over | 25 and over |
WHO splits obesity into class 1 (30–34.9), class 2 (35–39.9) and class 3 (40 and over), and calls 25–29.9 “pre-obesity”. NICE lowers each class by 2.5 for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, whose risk of type 2 diabetes and heart disease rises at a lower BMI. The Indian consensus doesn't name the range below 18.0, so the calculator shows it as below the normal range.
Why Asian and Indian cut-offs are lower
A WHO expert consultation in 2004 found that in many Asian populations a large share of people have a high risk of type 2 diabetes and heart disease at BMIs below 25. It kept the international categories but proposed extra action points at 23 and 27.5, which NICE now uses. Indian experts went further in 2009, setting overweight at 23 and obesity at 25 for Asian Indians. Their 2025 update keeps a BMI above 23 as the starting point for obesity, and adds waist size and effects on health to judge how serious it is.
What BMI can't tell you
- Muscle or fat. BMI can't tell them apart, so muscular people can read as overweight.
- Where fat sits. Fat around the waist carries more risk. NICE suggests also checking that your waist is less than half your height.
- Children and teenagers. They need BMI-for-age growth charts, not adult categories.
- Pregnancy and older age. Adult BMI isn't used in pregnancy, and NICE advises caution in people 65 and over.
Not medical advice
This calculator gives a number and the categories published for it, not a diagnosis. If your result worries you, or you're thinking about losing or gaining weight, talk to a doctor, who can look at your health as a whole.
Sources
Each link was last checked on .
- Nutrition: maintaining a healthy lifestyle, WHO Regional Office for Europe: the BMI formula and the adult BMI ranges for people over 20.
- Obesity and overweight (fact sheet), World Health Organization: adult overweight at 25 and obesity at 30; children use BMI-for-age instead.
- Adult BMI categories, US Centers for Disease Control and Prevention: adult categories for ages 20 and older, and obesity classes 1 to 3.
- Calculate your body mass index (BMI) for adults, NHS (2023): who shouldn't rely on adult BMI (under 18s, pregnancy, eating disorders) and that BMI can't tell muscle from fat.
- Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies, WHO Expert Consultation, The Lancet (2004): public health action points at BMI 23 and 27.5 for Asian populations.
- Overweight and obesity management (NG246), recommendations 1.9.10 to 1.9.13, NICE (2025): overweight from 23 and obesity from 27.5 for South Asian and other ethnic groups, and caution for muscular and older adults.
- Consensus statement for diagnosis of obesity, abdominal obesity and the metabolic syndrome for Asian Indians (Misra et al.), Journal of the Association of Physicians of India (2009): normal BMI 18.0–22.9, overweight 23.0–24.9 and obesity from 25 for Asian Indians.
- Revised definition of obesity in Asian Indians living in India (Misra et al.), Diabetes & Metabolic Syndrome: Clinical Research & Reviews (2025): the 2025 update that uses a BMI above 23 together with waist size and health effects.
Common uses
- Checking a health form. Insurance, gym and medical forms often ask for your BMI. Enter your height and weight in whichever units you know them and copy the result.
- Comparing WHO and Indian cut-offs. See the same BMI read against the WHO categories and the lower South Asian and Indian ones, which flag health risk at a lower BMI.
- Setting a weight goal. The healthy weight range for your height gives a sensible target to talk through with a doctor or dietitian before you start.