BMI Calculator
Free BMI calculator in metric and imperial units. Get your body mass index, the WHO category it falls in, and the weight range that would be healthy for your height.
What it does
Body mass index is your weight divided by the square of your height. It is a crude screening number, not a diagnosis: it was designed to describe populations, and it cannot tell muscle from fat. A heavily built athlete and someone carrying excess fat can land on the same figure. Read it as one input among several, not as a verdict.
WHO categories
| BMI | Category |
|---|---|
| < 16 | Severe thinness |
| 16 – 17 | Moderate thinness |
| 17 – 18.5 | Mild thinness |
| 18.5 – 25 | Normal weight |
| 25 – 30 | Overweight |
| 30 – 35 | Obese class I |
| 35 – 40 | Obese class II |
| ≥ 40 | Obese class III |
How to use it
- Choose metric or imperial units.
- Type your weight and your height.
- Read the index, the category and the weight range that matches your height.
The arithmetic runs in your browser. Nothing you type is sent anywhere and nothing is stored, so you can use these with real numbers.
Frequently asked questions
Is BMI accurate for everyone?
No. It ignores body composition, so it overstates risk for muscular people and understates it for people with little muscle. It is also read differently for children, for whom age and sex percentiles are used instead.
Which cut-offs does this use?
The World Health Organisation ranges for adults: under 18.5 underweight, 18.5 to 25 normal, 25 to 30 overweight, and three classes of obesity above 30. Some Asian health authorities use lower thresholds, so a local guideline may place the same number in a different band.
How is the healthy weight range worked out?
It is the weight that would put you at a BMI of 18.5 and at 25 for the height you entered — the two ends of the normal band, converted back into weight.
Does the calculation differ between metric and imperial?
No. Imperial values are converted using the exact definitions of the pound and the inch, so the same person gets the same index either way.
Wikipedia — Body mass index
Wikipedia — Obesity
Wikipedia — Body composition
Wikipedia — Adolphe Quetelet