Content reviewed: 24 September 2026
What BMI measures
Body mass index (BMI) relates weight to height using a simple mathematical ratio. It is commonly used as a population-level screening measure, but it is not a direct measurement of body fat and it does not diagnose health conditions.
Formula
Example
A person who weighs 70 kg and is 1.75 m tall has a BMI of about 22.9 because 70 ÷ (1.75 × 1.75) ≈ 22.9.
Why BMI has limitations
BMI does not distinguish muscle from fat, does not describe where body fat is distributed, and may be less informative for some athletes, older adults, pregnant people and others whose body composition differs from the assumptions behind the measure.
How to use the result
Treat BMI as one screening data point rather than a diagnosis. If you are making health or weight-management decisions, consider discussing the result with a qualified healthcare professional who can take your broader health context into account.
Read BMI and Calorie Estimates for more on what these numbers can and cannot tell you.