Lean body mass

Lean body mass (LBM), sometimes conflated with fat-free mass, is a component of body composition. Fat-free mass (FFM) is calculated by subtracting body fat weight from total body weight: total body weight is lean plus fat. In equations:

LBM = BW  BF
Lean body mass equals body weight minus body fat
LBM + BF = BW
Lean body mass plus body fat equals body weight

LBM differs from FFM in that cellular membranes are included in LBM although this is only a small percent difference in the body's mass (up to 3% in men and 5% in women)