Lean Body Mass
Calculator

Your weight with the fat removed. Muscle makes up most of it, along with bone, organs, water, and skin. When lifters talk about getting bigger, lean body mass is the number they mean. Scale weight alone hides how much of you is working tissue.

Boer is the most cited in clinical work and holds up well across body types. Hume lands close for most people. James was derived at moderate body fat levels and drifts when body fat runs high. This calculator averages all three, which smooths out the weakest assumptions of each one.

The fat-free mass index divides your lean mass in kilograms by your height in meters squared, so tall and short lifters can compare muscle mass fairly. A 1995 study of elite bodybuilders put 25 as the rough ceiling for drug-free men, with most trained men landing between 18 and 20. The normalized version adjusts the score for heights far from 1.8 meters.

Some of that drop is water and glycogen leaving the muscles, and it comes back when you eat more. Real muscle loss happens when the deficit runs steep or protein runs low. Keeping protein high and training hard through a cut holds onto most of your lean mass.

Progressive overload with enough protein to support it. Most lifters add lean mass slowly after the beginner phase, a few pounds a year with consistent training. Programs that raise the weight or the reps week after week are what drive the gain.

Muscle is the largest piece of lean body mass, sitting alongside bone, organs, and water. Skeletal muscle alone usually runs around half of total lean mass. When a formula estimates lean body mass, only part of the answer is contractile muscle tissue.