What BMI measures
Body Mass Index is a simple ratio of weight to height: weight (kg) ÷ height (m)². It was designed in the 1830s as a population-level statistical tool, not an individual diagnostic measurement — a distinction that gets lost in how it's commonly used today.
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
What BMI doesn't account for
Because BMI only uses height and weight, it can't distinguish between muscle and fat. A muscular athlete can register as "overweight" despite having low body fat, while someone with low muscle mass and higher body fat can fall in the "normal" range. BMI also doesn't account for age, sex, bone density, or how fat is distributed around the body — factors that matter for actual health risk.
BMI is a useful starting point for a conversation, not a diagnosis. If you have questions about what your number means for you specifically, a healthcare provider can put it in context alongside other measurements.
How to calculate your BMI
Enter your height and weight
The BMI Calculator supports both metric and imperial units.
Get your score instantly
See which standard category your result falls into.
Use it as one data point
Consider it alongside other health markers rather than in isolation.
Other measurements worth knowing about
Because of BMI's limitations, many health professionals also look at waist circumference, waist-to-hip ratio, or body composition measurements for a fuller picture. None of these — including BMI — replace an actual conversation with a healthcare provider about your individual health.
Calculate your BMI
Free, instant, and supports metric or imperial units.