Body Mass Index (BMI) is a relationship between weight and height that is associated with body fat and health risk. Body Mass Index (BMI) is a number calculated from a person's weight and height. BMI provides a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems.

For most people, BMI provides a good measure of obesity. However, BMI does not provide actual information on body composition (i.e. the proportions of muscle, bone, fat, and other tissues that make up a person’s total body weight), and may not be the most appropriate indicator to determine health status for certain groups of people.

Though BMI is generally a reliable approximation of body fat, it doesn't always tell the whole picture.