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.
Lean mass is what you protect on a cut — the coach builds the plan around it.
What is lean body mass?
Lean body mass (LBM) is everything that isn't fat — muscle, bone, organs, and water. It's the number that actually matters for protein needs and for tracking whether a cut is preserving the muscle you've 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 − bodyfat% / 100). The accuracy depends entirely on how good your body-fat estimate is.
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 are what make that happen. Want a plan that tracks lean mass over time and adjusts as you go? That's what the coach is for.