What this calculator measures
Lean body mass (LBM) is everything in your body that isn't fat — muscle, bone, organs, water, and connective tissue. Tracking LBM alongside total weight gives a much more accurate picture of training outcomes: a successful recomposition phase may show stable scale weight but a clear increase in LBM.
How this calculator works
Lean body mass = body weight × (1 − body fat% ÷ 100). This simple formula requires a reliable body fat percentage input — from the body fat calculator (Navy method) or another measurement source. The accuracy of the LBM figure depends directly on the accuracy of your body fat input.
How to use your result
Track LBM over time rather than at a single point. Losing body weight is only positive if LBM is being maintained or increased. If LBM drops alongside total weight, it signals insufficient protein, excessive deficit, or inadequate training stimulus. Combine with the protein calculator to ensure your intake supports muscle retention.
Why lean mass is the number worth protecting
During a calorie deficit the body draws on both fat and lean tissue. How much lean tissue it gives up depends largely on two things you control: protein intake and whether you keep lifting.
A diet that drops 8 kg of body weight with 7 kg from fat is a success. The same 8 kg with 4 kg from lean mass leaves you lighter, weaker, and with a lower daily energy expenditure than when you started.
The accuracy limits of this estimate
Lean body mass is only as good as the body-fat percentage it is built from. A tape-based estimate carries a few percentage points of error, and that error flows straight into the lean mass figure.
This makes the absolute number less useful than the trend. Measure the same way, at the same time of day, under the same conditions, and watch the direction it moves over months rather than treating any single result as exact.
Important limitation
Calculator results are estimates. Pregnancy, eating disorders, medical conditions, injuries, or concerning symptoms require qualified professional guidance.