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Estimate skeletal muscle mass, muscle mass percentage, and your Skeletal Muscle Mass Index (SMI) using the validated Lee (2000) equation.
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Skeletal muscle mass (SMM) is the weight of the muscles attached to your skeleton — the tissue you build with training. It is a subset of lean body mass, which also includes bone, organs, and water, so your muscle mass is always lower than your lean mass.
This calculator uses the Lee (2000) equation, which predicts total-body skeletal muscle from height, weight, age, sex, and ethnicity. It was validated against whole-body MRI in 244 adults (R² = 0.86, standard error ≈ 2.8 kg), so treat the result as a solid estimate rather than an exact measurement.
The Skeletal Muscle Mass Index (SMI) divides muscle mass by height squared, the same way BMI normalizes weight, and is the value clinicians screen against for low muscle mass (sarcopenia).
SMM (kg) = 0.244 × weight(kg) + 7.80 × height(m) + 6.6 × sex − 0.098 × age + ethnicity − 3.3 sex = 1 (male) or 0 (female); ethnicity = 0 White/Hispanic, −1.2 Asian, +1.4 African American SMI = SMM (kg) / height (m)²
No. Lean body mass is everything that is not fat — muscle plus bone, organs, and water. Skeletal muscle mass is only the muscle portion, so it is a smaller number. Skeletal muscle is roughly 30–40% of total body weight in healthy adults.
The Lee equation correlates strongly with MRI (R² = 0.86) with a standard error of about 2.8 kg. It is excellent for tracking changes over time, but a DEXA or MRI scan is more precise for a single snapshot.
Commonly used reference ranges are 8.51–10.75 kg/m² for men and 5.76–6.75 kg/m² for women. Below 8.50 (men) or 5.75 (women) indicates low muscle mass that may warrant a fuller sarcopenia assessment.
Progressive resistance training 2–4 times per week, 1.6–2.2 g of protein per kg of body weight per day, a small calorie surplus, and adequate sleep are the levers with the strongest evidence.