Lean body mass is everything you weigh except fat — muscle, bone, organs and water — typically 75–90% of body weight in men and 68–85% in women. This free calculator estimates yours with the Boer formula from height and weight; preserving lean mass through resistance training and adequate protein is one of the strongest predictors of healthy ageing.
Lean body mass is everything you weigh that isn’t fat: muscle, bone, organs, skin and water. It is the engine room of your metabolism, the reserve you draw on in illness, and the number that should stay stable — or grow — while body fat changes. This lean body mass calculator estimates yours with the Boer formula, the equation most validated for adults.
Calculate your lean mass below, then read on: the formulas, normal lean mass percentages, and why this number matters more with every decade of age.
Lean Body Mass
Boer formula: your muscle, bone and organ weight.
What is lean body mass?
Lean body mass (LBM) = total weight − fat mass. It includes skeletal muscle (the largest changeable part), bone, organs and body water. Two facts frame everything else: LBM drives most of your resting calorie burn — which is why our BMR calculator outputs track lean mass so closely — and adults lose 3–8% of muscle per decade after 30 unless they actively train against it.
Lean body mass formula (Boer)
Direct measurement needs a DEXA scan; formulas estimate from height and weight:
- Men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
- Women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3
The Boer equation is the one used in clinical contexts (including some drug dosing) because it tracks DEXA best across normal body sizes. If you already know your body fat percentage from our body fat calculator, you can also compute LBM directly as weight × (1 − body fat %) — when the two methods disagree meaningfully, trust the one built on a measured body fat value.
Normal lean body mass percentage
| Group | Typical LBM (% of body weight) |
|---|---|
| Men, healthy range | 75–90% |
| Women, healthy range | 68–85% |
| Male athletes | 85–93% |
| Female athletes | 80–87% |
These are simply the mirror image of body fat ranges — women’s healthy lean percentage is lower because essential fat is higher. The absolute number matters too: more lean kilograms mean a higher metabolism, stronger bones and better resilience.
LBM vs FFMI vs body fat percentage
Three related numbers, three different questions. Body fat % asks “how much of me is fat?” — the health question. LBM asks “how many kilograms of working tissue do I have?” — the metabolism and dosing question. FFMI asks “how muscular am I for my height?” — the training question. Together they describe your composition completely; any one alone can mislead.
Why lean mass matters more with age
Age-related muscle loss — sarcopenia — is one of the strongest predictors of frailty, falls and loss of independence in later life. The countermeasures are unglamorous and extremely effective: resistance training at any age (studies show meaningful gains even in the 80s and 90s) and adequate protein, around 1.0–1.2 g/kg daily for older adults — our protein calculator personalizes that. Preserving lean mass during weight loss is equally critical: aggressive diets without training shed muscle first, lowering the metabolism the diet depends on.
This tool is informational. It estimates body composition and does not diagnose any condition. Rapid unintentional loss of weight or muscle is a medical symptom that deserves a physician’s evaluation.
Frequently asked questions
What is a good lean body mass?
As a share of body weight: roughly 75–90% for men and 68–85% for women. Athletes sit at the top of those ranges. The trend over time matters more than any single value.
How do I calculate lean body mass?
Either with the Boer formula from height and weight (what this calculator does), or as weight × (1 − body fat %) if you have a measured body fat percentage.
How do I increase lean body mass?
Progressive resistance training plus 1.6–2.2 g of protein per kilogram daily and a small calorie surplus. Muscle accrues slowly — a kilogram in months, not weeks — and consistency beats intensity.
Does lean body mass include water?
Yes — body water sits within the lean compartment, which is why hydration swings can move bioimpedance lean-mass readings noticeably from day to day.
Why does lean body mass matter for medication dosing?
Several drugs distribute mainly in lean tissue, so dosing by total weight would overdose people with high body fat. Clinicians use lean-mass estimates for those specific drugs — always their calculation, not yours.
Numbers are a starting point — not a diagnosis
If your results raise questions, Acibadem specialists can review your situation properly: share your case and receive a free, no-obligation medical opinion from the relevant department.