Body Mass Index (BMI) is a metric used for measuring health. It’s calculated by dividing a person’ weight in kilograms by the square of the person’s height in meters. If you prefer to use English units, it’s your weight in pounds divided by the square of your height in inches, then multiplied by 703.
BMI doesn’t scale well. A tall man with the exact same build and body composition as a shorter man will have a higher BMI. Secondly, the measure ignores variation in body shapes. Some people are slender, others are stocky. Moreover, people carry fat in different places. Subcutaneous fat just below the skin is generally not associated with a steep rise in mortality, while abdominal fat is. Finally, BMI does not differentiate between fat and muscle mass. This glaring drawback means that many muscular athletes are considered overweight, or even obese. 1