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Body Composition

Skeletal Muscle Mass Calculator

Estimate your skeletal muscle mass using the validated Lee et al. formula — based on height, weight, age, sex, and ethnicity. Supports kg/lbs and cm/inches.

Skeletal Muscle Mass Estimator

Lee et al. formula (validated against MRI)

Unit System
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Estimated Skeletal Muscle Mass

The Lee et al. (2000) formula was derived from MRI validation studies and is one of the most accurate non-invasive methods to estimate skeletal muscle mass. It accounts for height, weight, age, sex, and ethnicity — all of which significantly influence muscle mass distribution.

Skeletal Muscle Index (SMI) Thresholds

CategoryMen (SMI kg/m²)Women (SMI kg/m²)
Sarcopenia (Low)< 7.26< 5.45
Normal7.26 – 9.505.45 – 7.50
Athletic> 9.50> 7.50

SMI = Skeletal Muscle Mass (kg) ÷ Height² (m²). Thresholds from EWGSOP (European Working Group on Sarcopenia in Older People).

Why Skeletal Muscle Mass Matters Beyond Aesthetics

Skeletal muscle is far more than an aesthetic tissue. It is metabolically active (burning calories at rest), functions as a glucose sink that improves insulin sensitivity, and serves as an amino acid reservoir during illness or injury. Higher skeletal muscle mass in older adults is strongly associated with lower all-cause mortality. This is why "muscle mass is the organ of longevity" — preserving SMM with age through resistance training is now recognised as a key preventive medicine strategy.

Frequently Asked Questions

Skeletal muscle mass (SMM) is the mass of all voluntary muscles that attach to the skeleton — the muscles you develop through training. It excludes smooth muscle (organs), cardiac muscle, bone mass, and body water. SMM typically accounts for 38–54% of body weight in trained men and 28–39% in women.
The Lee et al. formula has an R² of 0.88–0.92 when validated against MRI (the gold standard). It has an error of approximately ±2–3 kg for most individuals. Accuracy is lower for bodybuilders with extremely high muscle mass and very low fat, or for individuals with conditions affecting fluid balance.
Yes. Research consistently shows that older adults (50–80+) who begin resistance training gain significant skeletal muscle mass. Gains are slower than in younger people but remain meaningful. Protein intake becomes even more critical with age — aim for 1.8–2.2 g/kg body weight per day. Resistance training is the most potent available intervention against sarcopenia.
Either — select Metric or Imperial from the toggle. The calculator accepts kg/cm (metric, used in Europe) or lbs/inches (imperial, used in the USA). All unit conversion is handled automatically. The output shows your SMM in the same unit you selected, so you can track it consistently either way.

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