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How BMI is calculated
Body Mass Index divides your weight by the square of your height. The result is in kilograms per square metre.
BMI = 703 × weight (lb) ÷ height (in)²
Example: 68 kg and 1.70 m gives 68 ÷ (1.70 × 1.70) = 23.5.
BMI categories for adults
| BMI (kg/m²) | Category (WHO) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. A value under 1.0 means you are below that limit.
Frequently asked questions
What is a healthy BMI?
For adults, a BMI from 18.5 to 24.9 is classed as a healthy weight by the World Health Organization.
Is BMI accurate?
BMI is a quick screening number. It does not measure body fat directly and can misjudge very muscular people, older adults and some ethnic groups. Some Asian health bodies use lower cut-offs, such as 23 for overweight. Talk to a doctor for a full picture.
Can children use this BMI calculator?
No. For people under 20, BMI is read against age- and sex-specific percentile charts, not the adult categories used here.
Is my data stored?
No. The calculation happens in your browser and nothing you type is sent anywhere.