Before you attempt to calculate lean body mass, it is important to understand what it is. Lean body mass is comprised of the muscle, tendons, ligaments, bones, and organs in your body. Everything else is fat mass. In order to know how much lean body mass you contain, we need to know how much fat you contain since this an easy measurement to get though various body fat testing procedures. You can use skin fold calipers, bioelectrical impedance, or hydrostatic weighing (underwater weighing) to determine your body fat percentage. Skin fold and bioelectrical impedance measurements are generally easy to take yourself or have a trainer at your local gym take. Once you determine your body fat percentage, then it is just simple math to find the rest. Let’s say you are 150 pounds and 15% body fat. Multiply 150x.15 which equals 22.5. You have 22.5 pounds of fat on you. Then subtract the 22.5 from the original weight, 150-22.5. This equals 127.5. This tells you that at 150 pounds and 15% body fat, you have 127.5 pounds of lean body mass and 22.5 pounds of fat mass.