Lifestyle
Food & Nutrition
FitnessEstimate how much of your weight is muscle, bone, and organs.
This tool is for general information only and is not medical advice. Talk to a healthcare professional about results that concern you.
What Is Lean Body Mass?
Lean body mass (LBM) is everything you weigh except fat: muscle, bone, organs, skin, and water. For most healthy adults it makes up 60 to 90 percent of total weight. It is the metabolically active part of you, which is why two people at the same weight can have very different calorie needs and very different bodies.
This calculator runs three published formulas. Boer, the most widely used in medicine, is the headline number, with James and Hume shown for comparison. If you already know your body fat percentage, enter it and the calculator computes your LBM directly from it, which is more personal than any formula.
Why Lean Mass Is the Number Worth Protecting
- It drives your metabolism: each kilogram of muscle burns more calories at rest than fat does
- It is what crash diets destroy: fast weight loss without protein and training loses muscle along with fat
- It predicts healthy aging: muscle loss after 50 (sarcopenia) is a major driver of frailty, and it is preventable
- It is the honest progress metric: gaining weight while gaining lean mass is success, not failure
To keep or grow lean mass: strength train two to three times a week and eat enough protein. Our protein calculator gives you the gram target, and the body fat calculator gives you the percentage to feed into this tool.
Frequently Asked Questions
What is a good lean body mass percentage?
Typical healthy ranges are roughly 70 to 90 percent for men and 60 to 80 percent for women, the mirror image of healthy body fat ranges. Higher within the range generally means more muscle.
Is lean body mass the same as muscle mass?
No. LBM includes bones, organs, and water as well. Skeletal muscle is usually a bit under half of LBM. Gains in LBM from training, though, are mostly muscle, so tracking it works.
How do I use LBM for protein and calories?
Athletes often set protein by lean mass instead of total weight, around 2 to 2.4 g per kg of LBM, which avoids overshooting for people carrying more fat. The Katch-McArdle BMR formula also runs on LBM.
Can I gain lean mass while losing weight?
Yes, especially if you are new to lifting, returning after a break, or carrying higher body fat. A modest calorie deficit, high protein, and progressive strength training is the recipe for recomposition.
Sources
- Estimated lean body mass as an index for normalization of body fluid volumes in humans · PubMed (NLM/NIH) — Boer P, Am J Physiol 1984
- Prediction of lean body mass from height and weight · PubMed (NLM/NIH) — Hume R, J Clin Pathol 1966
- Relationship between total body water and surface area in normal and obese subjects · PubMed (NLM/NIH) — Hume R & Weyers E 1971 (basis of the James-type height-weight LBM equations)
- Lean Body Mass as a Predictor of Levothyroxine Requirement in Primary Hypothyroidism as Compared to Actual Body Weight · PubMed Central (NIH)
This calculator is for general information only and is not a substitute for professional medical advice.