What does Body Mass Index (BMI) primarily measure?

Body Mass Index (BMI) primarily measures the relationship between a person's weight and height, but it is particularly focused on estimating body fat. The calculation of BMI involves taking a person's weight in kilograms and dividing it by the square of their height in meters. This provides a numerical value that helps categorize individuals into different weight classes—underweight, normal weight, overweight, and obese—based on their body fat relative to their height and weight.

BMI is a useful tool for assessing whether an individual has a healthy body weight for a given height, which can help identify potential health risks related to being underweight or overweight. While it does not measure body fat directly, its associations with body fat and health outcomes make it a widely used metric in both clinical and public health contexts. This focus on weight and height ultimately underscores how BMI serves as a proxy for evaluating body fat levels across diverse populations.