Muscle Mass Calculator
Estimate skeletal muscle mass with the Lee equation from height, weight, age, and sex, plus lean body mass when you know your body fat percentage.
Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
Muscle Mass Calculator
Calculator
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Formula: Lee Equation: SM(kg) = 0.244 x BW + 7.80 x Ht(m) - 0.098 x Age + 6.6 x Sex - 3.3 | LBM = Weight x (1 - BF%)
Worked example — 31.9 kg muscle mass (42.5% of body weight)
Formula
Lee Equation: SM(kg) = 0.244 x BW + 7.80 x Ht(m) - 0.098 x Age + 6.6 x Sex - 3.3 | LBM = Weight x (1 - BF%)
The Lee equation estimates appendicular skeletal muscle mass from height, weight, age, and sex. Alternative: Lean Body Mass = total weight x (1 - body fat percentage). Average muscle mass: men 36-42% of body weight, women 29-35%.
Worked Examples
Example 1: 75kg male, 1.75m
Problem:75kg, 1.75m, 30yr, male
Solution:SM = 0.244(75) + 7.80(1.75) - 0.098(30) + 6.6(1) - 3.3 = 31.9 kg
Result:31.9 kg muscle mass (42.5% of body weight)
Frequently Asked Questions
What percentage of body weight is muscle?
Average skeletal muscle mass: men 36-42% of body weight, women 29-35%. Athletes may have 45-55%. Muscle mass declines 3-8% per decade after age 30 (sarcopenia).
What is the SMI threshold for sarcopenia?
Skeletal Muscle Index (SMI) = muscle mass / height². Low muscle mass: men <7.0 kg/m², women <5.4 kg/m² (per EWGSOP2 criteria). Also requires low strength or performance.
How can I increase muscle mass as I age?
Resistance training 2–4 times per week is the most effective intervention for preserving and building muscle mass at any age. Combine with adequate protein intake (1.6–2.0g/kg/day), sufficient calories, and quality sleep. Even older adults in their 70s and 80s can significantly increase muscle mass with progressive resistance training programs.
How accurate is the body fat percentage calculation?
The body fat percentage method (LBM = weight × [1 - BF%]) is only as accurate as your body fat measurement. Skinfold calipers: ±3–5%. Consumer bioelectrical impedance (bathroom scales): ±5–8%. DEXA scan: ±1–2% (gold standard). Hydrostatic weighing: ±1.5%. For most people, DEXA scans or multi-site skinfold measurements by a trained professional provide the best accuracy.
Why is the Skeletal Muscle Index divided by height squared?
Absolute muscle mass in kilograms scales with body size, so a tall person will always outrank a short one even at identical muscle quality. Dividing by height in metres squared normalises for frame, exactly as BMI does, giving a kg/m2 figure that can be tracked over time and set against reference values. Note that the low-muscle cut-points quoted on this page are defined on appendicular skeletal muscle, whereas the Lee equation estimates total-body skeletal muscle, so the comparison is indicative rather than diagnostic. For a 60 kg, 1.65 m, 45-year-old woman the Lee equation gives 19.8 kg of skeletal muscle, and 19.8 divided by 1.65 squared (2.7225) is an SMI of 7.3 kg/m2.
What is the difference between lean body mass and skeletal muscle mass?
Lean body mass is everything that is not fat: skeletal muscle plus bone mineral, organs, connective tissue and body water. Skeletal muscle is only a portion of it, typically somewhere near half in an average adult. That is why the LBM figure derived from your body fat percentage is always considerably larger than the Lee equation estimate on the same page. Comparing the two directly, or treating a gain in LBM as pure muscle, overstates real muscle change.
Why does the Lee equation include a separate sex term?
At the same height, weight and age, men carry more skeletal muscle and less fat than women, largely because of androgen exposure and differences in fat distribution. The equation captures this with a constant that is added for men and omitted for women, which is why entering 1 versus 0 for sex shifts the estimate by 6.6 kg. It is a population-average correction, so it fits a typical body composition better than an outlier one.
How is sarcopenia different from cachexia?
Sarcopenia is the progressive, largely age-related loss of skeletal muscle mass and strength, and it responds to resistance training and adequate protein. Cachexia is muscle wasting driven by an underlying illness such as cancer, heart failure or chronic kidney disease, involves systemic inflammation, and usually comes with unintentional weight and fat loss that nutrition alone does not reverse. A low estimate here says nothing about which is present; that distinction is a clinical assessment.
Why do bioelectrical impedance readings of muscle mass jump around day to day?
Bioelectrical impedance infers composition from how easily a current passes through the body, and current follows water and electrolytes. Muscle is roughly three-quarters water, so anything that shifts hydration, such as a recent meal, a hard training session, alcohol, or the time of day, changes the impedance and therefore the reported muscle mass. Measure under consistent conditions and treat the trend across weeks as the signal rather than any single reading.
Why does skeletal muscle mass matter beyond strength?
Skeletal muscle is the largest site of insulin-mediated glucose disposal, so more muscle generally means more capacity to clear glucose from the bloodstream. It is also metabolically active tissue contributing to resting energy expenditure, and it serves as the body's amino acid reserve during illness or injury. This is why preserving muscle through midlife and beyond is discussed as a metabolic and resilience goal, not only an aesthetic or athletic one.
References
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist · Editorial policy
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