About this tool
Why it exists.
Body mass index, or BMI, compares your weight with your height. It is a quick screening number used by doctors and public health bodies, but it is only a rough guide and does not show how much of your weight is fat or muscle.
Choose metric or imperial units, enter your height and weight, and the calculator shows your BMI, the adult category defined by the World Health Organization and the weight range that matches a BMI of 18.5 to 24.9 at your height. It is for adults only. For advice about your health, talk to a doctor or other qualified professional.
How to use it.
- Choose metric or imperial units.
- Enter your height and weight.
- Read your BMI, the category and the healthy weight range for your height.
Good questions.
What is the BMI formula?
BMI = weight in kilograms ÷ height in metres squared. For 70 kg and 170 cm, that is 70 ÷ 2.89, about 24.2.
What are the adult BMI categories?
The WHO uses under 18.5 for underweight, 18.5 to 24.9 for the healthy range, 25 to 29.9 for overweight and 30 or more for obesity.
Is BMI accurate for everyone?
No. It ignores muscle, bone, age, sex and ethnicity, and is not used for children, teenagers or pregnancy. Treat it as a starting point, not a diagnosis.