Body composition calculator
Lean body mass calculator
Split your body weight into lean mass and fat mass from your body-fat percentage. Free, instant, no sign-up.
Track this number — the trend says more than today's reading.
Free — no card, 30 seconds. Your result comes with you.
What is lean body mass?
Lean body mass (LBM) is everything that is not fat — muscle, bone, organs, and water. It is the number that matters for protein needs and for tracking whether a cut preserves the muscle you have built.
How this calculator works
Once you know your body-fat percentage, the rest is arithmetic. Fat mass is that fraction of your weight; lean body mass is the rest: LBM = weight × (1 − body-fat% / 100). The accuracy depends entirely on the quality of your body-fat estimate.
LBM, lean mass, and fat-free mass
LBM calculator, lean mass calculator, and fat-free mass calculator usually point to the same practical number: body weight minus fat mass. It is not pure muscle; it also includes water, organs, and bone. For training and nutrition, it is still a better anchor than scale weight alone.
Why it matters on a cut
The goal of a smart cut is to lose fat while keeping lean mass. Adequate protein and resistance training make that happen. The coach can track lean mass over time and adjust the plan as you go.