Muscle Mass Calculator
Inputs
Results
Muscle Mass (estimated)
Body Fat %
Fat Mass
Lean Body Mass
LBM (Boer)
BMI
FFMI
BMR (Mifflin–St Jeor)
Total Body Water
TDEE (est.)
Sources:
- Janssen I, Heymsfield SB, Wang Z, Ross R. Skeletal muscle mass and distribution in 468 men and women aged 18–88 yr . J Appl Physiol. 2000;89(1):81–88.
- Lee RC, Wang Z, Heo M, Ross R, Janssen I, Heymsfield SB. Total-body skeletal muscle mass: development and cross-validation of anthropometric prediction models . Am J Clin Nutr. 2000;72(3):796–803.
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes . Am J Physiol. 1984;247(4 Pt 2):F632–F636. (LBM reference)
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas . Br J Nutr. 1991;65(2):105–114. (body fat estimate)
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals . Am J Clin Nutr. 1990;51(2):241–247. (BMR estimate)
The Muscle Mass Calculator estimates how much of your body weight is skeletal muscle — the muscle attached to your bones that you build through training. Enter your height, weight, age, sex and (optionally) your body fat percentage; the tool returns an estimated skeletal muscle mass, lean body mass, and the share of your weight each represents.
Skeletal muscle typically makes up roughly 30–40% of total body weight in adults and is a strong indicator of metabolic health, strength and healthy aging. "Lean mass" is broader — it is everything that is not fat, including muscle, bone, organs and water — so it is always larger than skeletal muscle mass alone. If you leave the body fat field blank, the calculator estimates it from your profile, which lowers precision.
How it works
The calculator works in two steps:
- Lean body mass (LBM) is derived from your weight and body fat: fat mass = weight × body fat % , and lean mass = weight − fat mass . When body fat is not provided, it is first estimated with the Deurenberg equation (based on BMI, age and sex). An independent LBM estimate using the Boer equation is shown for comparison.
- Skeletal muscle mass is then approximated as a typical proportion of lean body mass — about 52% for men and 42% for women . The remaining lean tissue ("other lean") includes organs, bone and body fluids.
This proportion-based approach gives a quick educational estimate. It is not a substitute for direct measurement methods such as DXA, MRI or bioelectrical impedance, and it does not account for individual variation in bone density, hydration or limb proportions. For research-grade accuracy, anthropometric models that use limb circumferences and skinfolds (for example, Lee et al., 2000) or imaging are required.
Frequently Asked Questions
What's a healthy muscle mass percentage?
Skeletal muscle is roughly 30–35% of body weight for many women and 38–44% for many men, varying widely with age, genetics and training. Higher is generally better for strength and metabolic health, within a healthy body composition.
Muscle mass vs lean mass — what's the difference?
Lean mass includes bone, organs, water and muscle; skeletal muscle mass is only the muscle, so it is a subset of lean mass and always smaller.
How can I increase muscle mass?
Progressive resistance training, adequate protein intake (about 1.6–2.2 g per kg of body weight per day) and sufficient recovery and sleep are the main drivers of muscle growth.