Solo Biz Soft Editorial Team Body mass index (BMI) compares your weight with your height. It is a quick screening number that doctors and health services use for adults. Here is how to work it out and how to read the result.
The formula
Metric: BMI = weight in kilograms ÷ (height in metres × height in metres). Imperial: BMI = 703 × weight in pounds ÷ (height in inches)².
Step by step
- Measure your height and weight.
- Convert height to metres (or inches for the imperial formula).
- Square the height.
- Divide your weight by the squared height.
- Compare the result with the adult categories.
Worked example
A person 1.70 m tall weighing 70 kg: 1.70 × 1.70 = 2.89, and 70 ÷ 2.89 = 24.2, which is in the healthy weight range.
Common mistakes
- Using centimetres instead of metres
- Forgetting to square the height
- Treating BMI as a diagnosis. It is only a screening tool
Skip the maths: use our free BMI calculator. To estimate daily calories, try the calorie calculator.
Frequently asked questions
What are the adult BMI categories?
Under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, and 30 or more obese, according to the World Health Organization.
Is BMI accurate for athletes?
It can be misleading, because muscle weighs more than fat.
Should I use BMI for children?
No. Children use age and sex-specific growth charts. Ask a doctor.
More free tools: browse all our free calculators.
This article is general information and is not medical advice. Talk to a doctor about your health.