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Quick answer: Lean body mass is everything you weigh except fat: muscle, bone, organs, and water. For most men it runs 75 to 85 percent of body weight, for most women 65 to 75 percent. The calculator below estimates yours with the Boer, James, and Hume formulas.
Formulas estimate from height and weight. A DEXA scan is the gold standard if you need a measured number.
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Three clinical formulas estimate lean body mass from height, weight, and sex: Boer (1984), James (1976), and Hume (1966). Each was derived from body composition studies and each weighs height and weight slightly differently, so this calculator shows all three plus their average. Clinicians use these formulas for drug dosing research and body composition estimates when a scan is not available.
Formulas cannot see your individual build: two people with identical height and weight but different training histories carry different muscle. Treat the average as a solid baseline, and use a DEXA scan if you need precision, for example when tracking a serious recomposition phase.
| Group | Lean mass (share of body weight) |
|---|---|
| Men, typical range | 75 – 85% |
| Women, typical range | 65 – 75% |
| Trained male athletes | 85 – 90% |
| Trained female athletes | 75 – 85% |
Women naturally carry more essential fat (10 to 13 percent) than men (2 to 5 percent); that is physiology, not fitness.
Muscle is the only lean-mass component you can meaningfully grow. Consistent strength training adds it at roughly 0.5 to 2 pounds per month for newer lifters, slower with experience. Cardio maintains but rarely builds it.
Building lean mass requires enough protein (research supports 0.7 to 1 gram per pound for people training hard) and enough total food. In a steep calorie deficit, the body sheds muscle along with fat unless protein and training stay high.
Untrained adults lose 3 to 8 percent of muscle per decade after 30, a process called sarcopenia. The loss accelerates after 60 but responds remarkably well to lifting at any age; studies show meaningful muscle gain even in lifters starting in their 70s.
Boer, James, and Hume were built on different study populations decades apart. They typically land within a few pounds of each other for average builds and drift apart at very high or low body weights; James in particular overestimates at higher weights. The average of the three is a sensible compromise.
Lean body mass is your total weight minus fat mass: muscle, bone, organs, skin, and body water combined. It is not the same as muscle mass alone; muscle typically makes up about half of lean mass, with bone, organs, and water making up the rest.
Without a scan, use validated formulas that estimate from height, weight, and sex: Boer, James, and Hume are the three standards. For example, Boer for men is 0.407 times weight in kg plus 0.267 times height in cm minus 19.2. This calculator runs all three and averages them.
Lean body mass includes everything except fat, while muscle mass counts only skeletal muscle. A 150 lb person with 110 lb of lean mass might carry roughly 55 lb of actual muscle; the other lean pounds are bone, organs, and water. Gaining “lean mass” in practice usually means gaining muscle.
The Boer, James, and Hume formulas are the standard estimates and need only height, weight, and sex. Smart scales and handheld bioimpedance devices also estimate it, but their readings swing with hydration. For tracking progress, formulas plus a tape measure beat scale gadgets for consistency.
Typical lean mass is 75 to 85 percent of body weight for men and 65 to 75 percent for women, with athletes higher. More useful than any single target is direction: lean mass held or rising while weight falls means fat loss is going well.
For your safety
Estimate disclaimer: These formulas estimate lean mass from population studies; they are not measurements and are not validated for children or during pregnancy. At very high or very low body weights the formulas drift, and a DEXA scan ordered through a clinician is the reliable option.
Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
