BMI calculator
Enter your weight and height to get your body mass index and the WHO reference category. It is a rough indicator: to assess your health, always consult a healthcare professional.
BMI is calculated as weight ÷ height² (kg/m²).
What BMI is and what it's for
Body Mass Index (BMI) is a simple formula that relates weight to height: you divide weight in kilos by the square of height in metres. Someone weighing 70 kg who is 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. It's a screening tool designed for populations, a quick way to place a figure within reference ranges, not a diagnosis.
The WHO reference ranges
| Category | BMI (adults) |
|---|---|
| Underweight | below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obesity | 30 or above |
These are the ranges the World Health Organization uses for adults. They're meant to guide, not to label anyone.
Its limits, which matter
BMI has one big limitation: it only knows your weight and your height, not what that weight is made of. It doesn't tell muscle from fat, so a very muscular person can get a "high" BMI that means nothing worrying, while someone with little muscle can sit in the "normal" range without quite being so. It also ignores where fat is stored, age and sex, and it doesn't apply to children, teenagers, older adults, pregnant women or elite athletes, who are assessed by other criteria.