The Muscle Mass Calculator estimates your lean body mass (LBM) and an approximate skeletal muscle mass (SMM). If you enter body-fat percentage the calculator computes LBM directly from weight and body fat; otherwise it uses the Boer formula (a commonly used LBM estimate based on weight and height). SMM is then estimated as a percentage of LBM — many studies and population data place skeletal muscle at roughly 40–55% of LBM, so this tool defaults to 50% but lets you change that factor. These results are approximate — for accurate muscle mass measurement use DXA, MRI, or bioelectrical impedance performed by professionals and consult a healthcare or fitness specialist for interpretation.