BMI
Calculate your Body Mass Index and health category
These calculators provide general information only and are not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.
How to use BMI
- 1Choose your unit system: metric (centimetres / kilograms) or imperial (feet and inches / pounds).
- 2Enter your height and weight. Values are validated as you type, so you can preview the result before submitting.
- 3Read your BMI, the WHO category it falls into, and the healthy weight range for your height.
What is BMI and how is it calculated
BMI = weight (kg) ÷ height (m)²Body Mass Index relates body weight to the square of height and is used as a proxy for body fatness. It was introduced by the Belgian statistician Adolphe Quetelet in the 19th century and is still known as the Quetelet index. Because it needs only height and weight, it became the most widely used obesity screening tool worldwide.
BMI has well documented limits. It does not distinguish muscle from fat, and muscle is roughly 1.2 times denser than fat, so muscular athletes are often classed as overweight while older adults who have lost muscle may sit at a normal BMI despite high body fat. Asian populations also tend to carry more body fat at the same BMI, which is why several countries use lower cut-offs. Treat BMI as an initial screen and combine it with body fat percentage, waist circumference, blood pressure and lipid profiles.
| Category | BMI range (kg/m²) |
|---|---|
| Underweight | < 18.5 |
| Normal | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity class I | 30.0 – 34.9 |
| Obesity class II | 35.0 – 39.9 |
| Obesity class III | ≥ 40.0 |
BMI categories (WHO standard)
Frequently asked questions
Is BMI accurate for people who train with weights?
Not really. Muscle is denser than fat, so strength athletes often score above 25 while carrying little body fat. Body fat percentage is a better guide for them, ideally combined with waist circumference.
Do children use the same BMI cut-offs?
No. Children and adolescents aged 2 to 19 are assessed with age- and sex-specific BMI percentile curves rather than fixed adult thresholds. Interpretation belongs in the hands of a paediatrician.
Can I use this calculator during pregnancy?
It is not recommended. Weight changes during pregnancy reflect the baby, amniotic fluid and blood volume, so BMI no longer applies. Follow your obstetrician's guidance, which sets weight-gain targets based on pre-pregnancy BMI.
Does a normal BMI guarantee good health?
No. It is common to have a normal BMI with excess visceral fat, and the metabolic risk in that group is often underestimated. Combine BMI with waist circumference and body fat percentage for a fuller picture.