Body Mass Index (BMI) is a quick screening number that compares weight with height. This calculator works with kilograms and centimetres or pounds, feet and inches, tells you which standard adult category your result falls into, and shows the weight range that counts as “healthy” for your height.
How to use it
- Choose metric or imperial units.
- Enter your weight and height.
- Click “Calculate BMI” to see your number, category and healthy range.
The BMI formula
BMI = 703 × weight (lb) ÷ height (in)²
For example, someone who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.
Adult BMI categories
- Below 18.5 – underweight
- 18.5 to 24.9 – healthy weight
- 25 to 29.9 – overweight
- 30 and above – obesity
These are the World Health Organization ranges for adults aged 18 and over. Some health services use lower cut-offs for people of South Asian, Chinese and other Asian backgrounds, because health risks start to rise at a lower BMI.
What BMI does not tell you
BMI does not separate muscle from fat, so athletes can score as “overweight” while being very fit. It also ignores where fat is stored, age and sex. Treat it as a starting point and speak to a doctor or qualified health professional about your own health.
Frequently asked questions
Can children use this calculator?
No. Children and teenagers need BMI-for-age percentiles, which compare them with others of the same age and sex. Ask a pediatrician for that check.
Is BMI accurate during pregnancy?
No. Weight gain in pregnancy is expected, so BMI is not a useful measure at that time.
This calculator is for general information only and is not medical advice.