How much muscle do you have? This free muscle mass calculator estimates your skeletal muscle mass from height, weight, age and sex, with its percentage of body weight and your lean mass for context.
This estimates skeletal muscle mass from height, weight, age and sex using a published anthropometric equation. It’s an approximation, not a body-composition scan.
An estimate only – formulas can’t see your real composition. Methods like DEXA or BIA are far more accurate. Healthy muscle mass varies widely by build, training and genetics.
How the Muscle Mass Calculator Works
This calculator estimates your skeletal muscle mass (SMM) from your height, weight, age and sex, using a published anthropometric equation rather than a body scan. It also reports what share of your body weight that muscle represents, an estimated lean body mass figure, and a height-adjusted muscle index.
Formula (Lee, 2000): SMM (kg) = 0.244 × Weight (kg) + 7.80 × Height (m) + 6.6 × Sex − 0.098 × Age − 3.3, where Sex = 1 for male and 0 for female. Muscle % of body weight = SMM ÷ Weight × 100. The muscle index (SMI) = SMM ÷ Height (m)². Lean body mass is estimated separately using the Boer equation: for males, 0.407 × Weight (kg) + 0.267 × Height (cm) − 19.2; for females, 0.252 × Weight (kg) + 0.473 × Height (cm) − 48.3.
- Sex — male or female, which sets the sex term in the SMM formula and which Boer equation variant is used.
- Height — entered in cm (metric) or feet and inches (imperial); converted to meters for the SMM and SMI formulas.
- Weight — entered in kg or lb; converted to kilograms before any calculation.
- Age — in years; muscle mass is estimated to decline slightly as age increases in this formula.
Example Scenarios
| Sex | Height | Weight | Age | Estimated Skeletal Muscle Mass |
|---|---|---|---|---|
| Male | 178 cm | 75 kg | 30 | 32.5 kg (43.4% of body weight) |
| Female | 165 cm | 60 kg | 25 | 21.8 kg (36.3% of body weight) |
| Male | 185 cm | 90 kg | 45 | 35.3 kg (39.2% of body weight) |
| Female | 160 cm | 55 kg | 50 | 17.7 kg (32.2% of body weight) |
How to Interpret a Muscle Mass Calculator Estimate
A muscle mass calculator predicts skeletal muscle from height, weight, age and sex using an equation developed in a study population. It does not measure you directly, so treat the result as a reasonable estimate.
- Formula estimates tend to stray most for very muscular people and for those with higher body fat, so a muscle mass calculator may misjudge both groups.
- Use it for context, not progress tracking. Because the estimate comes from your stats rather than a scan, a muscle mass calculator cannot see muscle you gain while your weight stays the same.
More precise options include DEXA scans, bioelectrical impedance devices and, in research, MRI. If a muscle mass calculator result seems low for your age, or you notice unexplained weakness or weight loss, talk to a doctor; age-related muscle loss is common and can often be slowed.
Strength training and enough protein support muscle at any age. The lean body mass article on Wikipedia explains how lean mass differs from skeletal muscle, a useful distinction when reading a muscle mass calculator.
Muscle Mass Calculator FAQ
What is skeletal muscle mass and how is it different from lean body mass?
Skeletal muscle mass is just the muscle attached to your bones that you can move voluntarily. Lean body mass is broader — it includes muscle plus organs, bone, water and everything else that isn’t fat. This calculator estimates both, separately.Why does age lower the estimated muscle mass?
The underlying equation subtracts a small amount for each year of age, reflecting the general tendency for skeletal muscle to gradually decline over adulthood absent training. It’s a population-level pattern built into the formula, not a measurement of your individual muscle loss.How accurate is a muscle mass formula compared to a body scan?
Formula-based estimates like this one are far less precise than methods such as DEXA or bioelectrical impedance (BIA) analysis, which directly measure tissue. Treat the result as a general reference point rather than a clinical body-composition reading.What counts as a healthy percentage of muscle mass?
There’s no single universal target — healthy muscle percentage varies widely with sex, body frame, training history and genetics. This calculator shows your estimated share of body weight so you can track your own trend over time rather than compare against a fixed number.What is the SMI (muscle index) number for?
SMI divides your estimated skeletal muscle mass by your height in meters squared, similar to how BMI adjusts weight for height. It’s a way to compare muscle mass across people of different heights on a more even footing.Why do I need to enter both height and weight?
The Lee equation combines height and weight because taller, heavier frames typically carry more absolute muscle mass. Using both, along with age and sex, gives a more representative estimate than weight or height alone.Related Calculators
Muscle mass is only part of the body-composition picture — pair this estimate with the body fat calculator or the lean body mass calculator for a fuller view. If you’re training to build muscle, the protein calculator can help set a daily protein target to support it.