On this page
What BMI measures
BMI measures weight relative to height. It doesn't measure body fat directly, but for most adults it rises and falls with body fat, which is why it's used as a quick screening number.1 Dividing by height squared means tall and short people can be compared on the same scale. Why height is squared.
How to calculate it
BMI = weight (kg) ÷ height (m)²
BMI = 703 × weight (lb) ÷ height (in)²
For someone who is 1.70 m and 65 kg: 65 ÷ (1.70 × 1.70) = 22.5. The calculator at the top does this for you and shows each step. How to calculate BMI.
What the number means
For adults, these are the standard categories set by the WHO and used by the CDC.21
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25–29.9 | Overweight |
| 30 and above | Obesity |
Children and teens are assessed differently, by percentile for age and sex.1 BMI categories in detail.
Where BMI is used
- Doctors' offices, as a quick first check at routine visits.
- Public health, to track weight trends across whole populations.
- Research, where it's the most common way to group people by weight.
- Insurance, where some life and health insurers use height-and-weight measures in their applications.
Frequently asked questions
What does BMI stand for?
Body mass index.
Is BMI the same as body fat percentage?
No. BMI uses only height and weight. Body fat percentage is the share of your weight that's fat. BMI vs. body fat.
Is BMI the same for men and women?
Yes, adults use the same formula and categories. What BMI can and can't tell you.
Sources
This page is for education and is not medical advice. Talk with a healthcare professional about your weight and health.
