The body mass index (BMI) is used to assess a person's body weight relative to height. It's a useful, indirect measure of body composition and is a helpful indicator of obesity and underweight in adults. BMI compares well to body fat but cannot be interpreted as a certain percentage of body fat. Also, the relation between fatness and BMI is influenced by age and gender.
Some people with dense muscle mass may have a high BMI score but very little body fat. For them, waist circumference, skinfold or fatfold measurements, or more direct methods of measuring body fat may be more useful measures.|