BMI Calculator (Body Mass Index)
Body Mass Index relates weight and height and serves as a first population-level reference. We show your value, the World Health Organization category it falls into, and what weight range would correspond to your height.
The BMI formula
Weight (kg) ÷ Height (m)²18.5 ≤ BMI < 25Height goes in meters: 170 cm is 1.70 m, and the square is 2.89.
Source: World Health Organization (WHO) BMI classification.
Example
A person weighing 70 kg at 170 cm: 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2. That is within the normal weight range, whose upper limit for that height is around 72 kg.
Frequently asked questions
Does BMI work for everyone?
It's a population-level indicator, not an individual one. It doesn't distinguish between muscle and fat, so it can classify very muscular people as overweight, and it doesn't account for where fat is stored, which is what's most linked to cardiovascular risk.
What are the WHO ranges?
Underweight below 18.5. Normal weight between 18.5 and 24.9. Overweight between 25 and 29.9. Obesity class I between 30 and 34.9, class II between 35 and 39.9, and class III from 40 upward.
Does it apply to children or older adults?
Under-18s use age- and sex-specific percentiles, not the adult ranges. Interpretation also changes for older adults. In both cases, a healthcare professional's assessment is recommended.