How is body mass index calculated?

Body Mass Index (BMI) is a tool used to estimate total body fat by calculating an individual's weight in relation to their height.12

The formula for calculating BMI is:

$$\text{BMI}=\frac{\text{weight (kg)}}{{\text{height (m)}}^2}$$

In this calculation, weight is measured in kilograms and height is measured in metres.12

While BMI is a standard metric for identifying obesity—typically defined for adults as a score of 30.0 or higher—it is important to note that it is not a direct measure of body fat. Because the index does not account for factors such as muscle mass, bone density, or body fat distribution, medical organizations like the American Medical Association have cautioned against relying on it as the sole indicator of a patient's health.12