BMI Calculator
Calculate your body mass index from your height and weight — with the WHO category, the healthy weight range for your height and how far you are from it.
| Category | BMI | Weight for your height |
|---|
For healthy adults. These are estimates, not medical advice. Ask a doctor or dietitian about your own targets — especially if you are pregnant, have a health condition or are under 18.
What is BMI?
Body mass index (BMI) compares your weight with your height. It is a quick screening number used by doctors and health organisations to sort adults into weight categories — not a measure of body fat or health on its own.
BMI formula
BMI = 703 × weight (lb) ÷ height (in)²
Example: 75 kg at 1.75 m gives 75 ÷ 1.75² = 24.5, a healthy weight. In US units, 160 lb at 5 ft 9 in (69 in) gives 703 × 160 ÷ 69² = 23.6.
BMI categories for adults
| BMI | Category (WHO) |
|---|---|
| below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40 or more | Obesity class III |
Limits of BMI
- Muscle: muscular people can have a high BMI with little body fat.
- Age and ethnicity: older adults lose muscle, and people of South Asian, Chinese and some other backgrounds have higher health risks at a lower BMI — some guidelines use 23 and 27.5 as thresholds for them.
- Children and teens: BMI is read on age- and sex-specific percentile charts, so the adult categories above do not apply under 18.
- Pregnancy: BMI is not used to judge weight during pregnancy.
For a fuller picture, combine BMI with your waist size or a body fat estimate, and talk to a doctor about what is right for you.
Frequently asked questions
How do I calculate BMI?
Divide your weight in kilograms by your height in metres squared. With 70 kg and 1.70 m: 70 ÷ 2.89 = 24.2.
What is a healthy BMI?
For adults, 18.5 to 24.9 is the healthy weight range according to the WHO.
Is BMI different for men and women?
The adult formula and categories are the same for men and women. Women tend to have more body fat at the same BMI.
Is BMI accurate for athletes?
Not very. Muscle weighs more than fat, so athletes can be classed as overweight while having little body fat. A body fat estimate is more useful for them.