Lean Body Mass Calculator
Break your body weight into lean mass and fat mass, then use that result to guide protein targets, FFMI interpretation, and body-composition planning.
Lean body mass = body weight × (1 − body fat %) · Fat mass = body weight − lean body mass
Clear numbers first, practical next steps after.
Every calculator is built to give you an estimate you can actually use for nutrition, training, or body-composition planning.
Use your best estimate. The output is only as good as the body-fat input.
Why lean body mass matters
Scale weight alone cannot tell you whether a change came from fat, lean tissue, or water. Lean body mass gives you a better baseline for interpreting weight changes.
It is especially useful when paired with FFMI, waist data, and training performance. Together they show whether a phase is preserving or improving lean tissue.
How to track LBM over time
Do not overreact to weekly noise. Body-fat estimates move around. The most useful approach is to compare trends over a month or a training block.
If body weight falls but lean body mass stays roughly stable, your cut is likely preserving muscle well enough.
Frequently Asked Questions
What is lean body mass?
Lean body mass is everything in your body that is not fat. That includes muscle, bone, organs, water, and connective tissue.
Is lean body mass the same as muscle mass?
No. Muscle is part of lean body mass, but lean body mass includes more than muscle alone. That is why LBM is useful but not identical to direct muscle estimates.
Why use lean body mass for nutrition?
LBM can make protein and deficit planning more specific, especially during cuts where preserving lean tissue is the priority.
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See lean mass trends instead of guessing
Log body weight, measurements, and calculator outputs together so your lean-mass trend tells a coherent story over time.