Enter your height and weight to find your Body Mass Index and category.
Body mass index is weight divided by height squared. It was devised in the 1830s by the Belgian statistician Adolphe Quetelet as a way of describing populations, not individuals — a point worth holding onto, because it explains most of what follows.
A person weighing 72 kg at 1.68 m:
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 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 and above |
These thresholds are not universal. For people of South Asian, Chinese and other Asian ancestry, metabolic risk rises at lower BMI values, so many health authorities use 23 as the overweight threshold and 27.5 for obesity. Applying the standard cut-offs to these populations substantially understates risk.
BMI knows two numbers, and everything it cannot distinguish follows from that.
BMI is most useful alongside a measure of fat distribution, which is where the actual risk signal lives.
Clinical markers — blood pressure, fasting glucose, cholesterol — tell you more than any of these anthropometric numbers, and none of them requires a calculator's interpretation.
Given all that, BMI persists because it is cheap, requires only a scale and a tape, is consistent between observers, and works well for what it was built for: comparing groups. Population-level BMI trends track health outcomes reliably. The error is in treating a population statistic as a diagnosis of an individual.
This is an estimate, not medical advice. A BMI outside the healthy range is a prompt for a conversation with a doctor, not a diagnosis in itself — and a BMI inside it is not a clean bill of health.
No. Muscle is denser than fat, so muscular people frequently register as overweight or obese while carrying very little body fat. Body fat percentage or waist measurement is far more informative for anyone who trains seriously.
Because metabolic risk — particularly type 2 diabetes and cardiovascular disease — rises at lower BMI values in people of South Asian, Chinese and other Asian ancestry. Many authorities use 23 for overweight and 27.5 for obesity rather than 25 and 30.
Not with adult categories. Children are assessed against age-and-sex-specific percentile charts, since healthy body composition changes substantially through growth. Use a paediatric growth chart instead.
Waist-to-height ratio is simple and predicts cardiovascular risk better — keeping your waist under half your height is the guide. Waist circumference and body fat percentage are also more informative, and clinical markers such as blood pressure and fasting glucose more informative still.
Because dividing by height squared does not match how bodies actually scale. The formula systematically reads slightly high for tall people and slightly low for short ones — a known limitation of Quetelet's original population statistic.