Skeletal Muscle Mass Calculator
Estimate skeletal muscle mass in kg from weight, height, age, sex and ancestry with the Lee equation, plus muscle as a percentage of body weight and the skeletal muscle index used to screen for sarcopenia.
How it works
SM (kg) = 0.244 × weight (kg) + 7.80 × height (m) + 6.6 × sex − 0.098 × age + ancestry − 3.3 (sex: men 1, women 0; ancestry: Asian −1.2, African descent +1.4, other 0) · SMI = SM ÷ height²
Lee and colleagues (American Journal of Clinical Nutrition, 2000) calibrated this anthropometric equation against whole-body MRI in 244 adults; it explains about 86% of the variation in skeletal muscle mass with an error of about 2.8 kg. Dividing by height squared gives the skeletal muscle index, and Janssen et al. (2004) linked low values to physical disability in older adults. Because the equation relies on body weight, it overestimates muscle in people with obesity.
Worked example
A 35-year-old man of 80 kg and 178 cm: SM = 0.244 × 80 + 7.80 × 1.78 + 6.6 − 0.098 × 35 + 0 − 3.3 = 33.3 kg, which is 41.6% of body weight and an index of 33.3 ÷ 1.78² = 10.50 kg/m² (moderate-risk band, 8.51–10.75).
Sources: Lee RC et al. Total-body skeletal muscle mass: development and cross-validation of anthropometric prediction models. Am J Clin Nutr 2000 · Janssen I et al. Skeletal muscle cutpoints associated with elevated physical disability risk in older men and women. Am J Epidemiol 2004
Frequently asked questions
How much skeletal muscle mass should I have?
Healthy young adult men typically carry 33–40% of body weight as skeletal muscle and women 25–32%. The skeletal muscle index adjusts for height: above about 10.75 kg/m² for men and 6.75 kg/m² for women is low risk in Janssen's cut-offs.
Is skeletal muscle mass the same as lean body mass?
No. Lean body mass includes organs, bone, blood and water; skeletal muscle is only the muscle attached to the skeleton, usually about half of lean mass.
What is sarcopenia?
Age-related loss of muscle mass and strength. Diagnosis combines low muscle mass with low grip strength or slow walking speed — an equation alone cannot diagnose it.
Why does ancestry appear in the equation?
The MRI study found small average differences in muscle mass at the same height and weight between groups, so Lee added a correction term. It is a population average, not a rule for individuals.
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This calculator gives an estimate for general fitness and education only. It is not a diagnosis — results from field tests and prediction equations can differ from laboratory measurements, so talk to a doctor or qualified exercise professional before acting on them.