How to use the BMI calculator
Choose metric or imperial, then enter your weight and height. You get your BMI, your category, the healthy weight range for your height and how far you are from it. Asian cut-offs are available for people of South Asian, East Asian or Southeast Asian descent.
BMI formula
BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²
The calculator converts imperial units to kilograms and metres exactly (1 lb = 0.45359237 kg, 1 in = 2.54 cm), so both give the same answer.
Worked example
Someone who weighs 70 kg and is 175 cm tall: 1.75 × 1.75 = 3.0625. BMI = 70 ÷ 3.0625 = 22.9, a healthy weight.
In imperial, 154 lb and 5 ft 9 in (69 in): 703 × 154 ÷ 69² = 22.7. The small difference is because 154 lb and 69 in are rounded.
BMI categories for adults
| Category | Standard (WHO) | Asian (WHO action points) |
|---|---|---|
| Underweight | Under 18.5 | Under 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 27.4 |
| Obese | 30 or more | 27.5 or more |
The Asian cut-offs come from a WHO expert consultation and are used by health services such as the NHS (UK) and in India's national guidelines (which use 23 and 25).
What BMI can't tell you
- It doesn't separate muscle from fat, so muscular people can show as overweight.
- It doesn't show where fat sits. Waist size matters too: the NHS suggests a waist under half your height.
- For children and teenagers, BMI is compared with growth charts for their age and sex instead of these adult categories.
Want to know how many calories you need? Try the calorie calculator.
Frequently asked questions
What is a healthy BMI?
For most adults, 18.5 to 24.9. For people of Asian descent, many health services use 18.5 to 22.9.
Is BMI different for men and women?
No. The adult formula and categories are the same for everyone, although women tend to carry more body fat at the same BMI.
What is BMI Prime?
Your BMI divided by the upper limit of the healthy range (25, or 23 with Asian cut-offs). Under 1.0 means you're below the upper limit.
Sources
Formulas checked 29 October 2026. How we test our calculators. This calculator gives general estimates for adults and is not medical advice. Talk to a doctor or dietitian about your own health.