How do you use the body mass index to determine your fat?

Measuring your body mass cannot directly determine your overall body fat. BMI, or Body Mass Index, is designed to determine a healthy weight of a person based on their overall height, age and gender. The reason this index cannot determine your precise body fat is that individuals as the same height with the same BMI may have different body types resulting in the same weight. Overall BMI assists with determining a healthy weight but cannot actually measure you in muscle or fat.