How to use it
- Choose metric (kilograms and centimetres) or US units (pounds, feet and inches).
- Enter your weight and height. Decimals work with a dot or a comma.
- Read your BMI, its category and the healthy weight range for your height.
How BMI is calculated
Body mass index is your weight in kilograms divided by the square of your height in metres:
BMI = weight (kg) ÷ height (m)²
For US units the calculator first converts: 1 lb = 0.45359237 kg and 1 in = 2.54 cm, both exact. The healthy range is the weight that gives a BMI of 18.5 to 24.9 at your height: 18.5 × height² to 24.9 × height².
| BMI | Category (adults, WHO) |
|---|---|
| below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obesity |
Worked example
A person who weighs 70 kg and is 175 cm tall: 1.75² = 3.0625, and 70 ÷ 3.0625 = 22.9, a healthy weight. For that height the healthy range is 18.5 × 3.0625 = 56.7 kg to 24.9 × 3.0625 = 76.3 kg.
What BMI does not tell you
BMI is a quick screening number for adults, not a diagnosis. It does not separate muscle from fat, says nothing about where fat sits, and is not meant for children, pregnant women or very muscular people. If your result worries you, talk to a doctor, who can look at waist size, blood pressure and other measures.