Muscle Mass Calculator

Your skeletal muscle mass (SMM) is the portion of your lean body mass made up of the voluntary muscles you train and move with. It is a key marker of strength, metabolic health, and healthy ageing. This calculator gives a population-equation estimate of SMM from your height, weight, age, and sex, then expresses it as a share of your body weight.

The Approach

Direct SMM measurement needs MRI or DEXA. In their absence, anthropometric equations such as those by Janssen and Lee predict SMM from body size and demographics. We use a simplified prediction of the same form:

Here sex = 1 for men and 0 for women, reflecting men's higher average muscle mass.

Worked Example

A 30-year-old man, 80 kg, 1.80 m:

• 0.244×80 = 19.5; 7.8×1.80 = 14.0; sex term +6.6; age −2.94
• SMM ≈ 34 kg after the sex offset
• Muscle share = 34 / 80 × 100 ≈ 42% of body weight

Typical Muscle-Mass Share

Why Muscle Mass Matters

Muscle is metabolically active tissue: more of it raises resting energy expenditure, improves insulin sensitivity, and supports bone density. From around age 30 adults lose muscle steadily (sarcopenia) unless they train — which is why tracking SMM and resistance training become more important with age.

Limits of the Estimate

Anthropometric equations assume an "average" build, so they under-read for very muscular athletes and over-read for the very sedentary. Treat the figure as a ballpark and a trend line, not an exact measurement — for precision, use DEXA or a research-grade BIA device.

Note: This is an informational estimate of skeletal muscle from body size and demographics, not a clinical measurement or diagnosis. For medical concerns about muscle loss, consult a healthcare professional.