What is lean body mass?

Lean body mass (LBM) is the total weight of everything in your body except fat: muscles, bones, organs, blood, skin, and water. LBM is not the same as muscle mass — it includes bones, organs, and water in addition to skeletal muscle. LBM is used in clinical medicine for drug dosing calculations and is a key marker in body composition assessment.

What is a good lean body mass percentage?

LBM percentage = 100% minus body fat percentage. For men: athletic is 80-90% LBM (10-20% fat), average is 74-80% (20-26% fat), obese is below 67% (33%+ fat). For women: athletic is 78-85% LBM (15-22% fat), average is 68-78% (22-32% fat). These ranges are approximations — optimal LBM depends on individual factors.

Why is lean body mass important?

LBM is important for: calorie needs calculation (muscle is metabolically active); medication dosing (many drugs dosed by LBM not total weight); athletic performance assessment; tracking body recomposition progress; and clinical nutrition planning. Katch-McArdle BMR formula uses LBM directly for the most accurate metabolic rate estimation.

How do I increase lean body mass?

To increase LBM: resistance training at least 3x per week targeting all major muscle groups; adequate protein intake (0.7-1.0g per pound of body weight); calorie surplus (200-300 calories above maintenance for lean gaining); adequate sleep (7-9 hours); and progressive overload in training. Building significant LBM takes months to years of consistent effort.

Lean Body Mass Calculator

Calculate your lean body mass (LBM) — the weight of everything in your body except fat — using 5 validated formulas. See your body composition breakdown and how LBM relates to your calorie needs, protein targets, and metabolic rate.

Your Lean Body Mass

              LBM (Boer formula)
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Formula Average —

Fat Mass —

Body Fat % —

LBM by Formula Comparison

Formula	LBM	Fat Mass	Body Fat %	Notes

What Your LBM Means

Metric	Your Value	Notes

LBM Formulas Explained

These formulas estimate LBM from height and weight — without needing body fat measurement. Each was developed from different population samples, which is why results can vary by 3–5%.

Boer (1984): Male: 0.407×W + 0.267×H − 19.2; Female: 0.252×W + 0.473×H − 48.3 (W=kg, H=cm)
James (1976): Male: 1.1×W − 128×(W/H)²; Female: 1.07×W − 148×(W/H)²
Hume (1966): Male: 0.3281×W + 0.33929×H − 29.5336; Female: 0.29569×W + 0.41813×H − 43.2933
Peters (1994): Male: 3.8 × 0.0215 × W⁰·⁶⁵⁶ × H⁰·⁷³³; Female: uses same with lower factor

The Boer formula is most widely used in clinical pharmacokinetics. The Katch-McArdle formula (if body fat % is known) is most accurate: LBM = Total Weight × (1 − Body Fat%).

What Lean Body Mass Tells You

Lean body mass (LBM) is total body weight minus fat — it includes muscle, bone, organs, water, and connective tissue. Unlike body weight, LBM is a more stable indicator of fitness progress. When strength training effectively, LBM increases while fat mass decreases even if total weight stays similar.

LBM is used in nutritional planning (protein targets are often set at 0.7–1g per pound of LBM), medication dosing, and metabolic assessments. Tracking LBM over weeks gives a clearer picture of body recomposition than the scale alone.

Frequently Asked Questions

LBM percentage = 100% minus body fat percentage. For men, 85–92% LBM (8–15% body fat) is athletic to healthy. For women, 75–85% LBM (15–25% body fat) is typical for healthy active individuals. Elite athletes can exceed these ranges.

Formulas (Boer, James, Hume) are population-average estimates using height and weight. They can overestimate LBM in obese individuals and underestimate it in highly muscular athletes. DEXA scans or hydrostatic weighing are more precise but require specialized equipment.

Progressive resistance training 3–4 times per week is the most effective method. Adequate protein (0.7–1g per pound of bodyweight), slight caloric surplus or maintenance, and sufficient sleep (where most muscle protein synthesis occurs) complete the formula. Results are visible after 8–12 consistent weeks.

Yes. The Boer, James, and Hume formulas estimate LBM from height and weight alone — no body fat measurement needed. These are population-average estimates and carry an error of roughly ±3–5 kg. If you know your body fat percentage from a DEXA scan or calipers, the Katch-McArdle formula (LBM = weight × (1 − BF%)) will give you a more accurate result.

Height: 177.8 cm, Weight: 79.4 kg. Using the Boer formula: LBM = 0.407 × 79.4 + 0.267 × 177.8 − 19.2 = 32.3 + 47.5 − 19.2 = 60.6 kg (133.5 lbs). Estimated fat mass = 79.4 − 60.6 = 18.8 kg (41.4 lbs), giving a body fat of about 23.6%. Protein target at 0.82 g/lb LBM = 133.5 × 0.82 = 110 g/day. Katch-McArdle BMR = 370 + 21.6 × 60.6 = 1,679 kcal/day.