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Lean Body Mass CalculatorHow it works
Lean body mass (LBM) is the weight of everything in your body except fat — muscle, bone, organs, water, and connective tissue. It's a key input for accurate TDEE calculations (Katch-McArdle formula), medication dosing in clinical settings, and tracking muscle gain independently of overall weight changes. The Lean Body Mass Calculator estimates LBM using circumference-based and BMI-based formulas.
Formulas calculated:
**Boer formula** (circumference-based): - Men: (0.407 × weight kg) + (0.267 × height cm) − 19.2 - Women: (0.252 × weight kg) + (0.473 × height cm) − 48.3
**James formula**: - Men: (1.1 × weight kg) − 128 × (weight kg ÷ height cm)² - Women: (1.07 × weight kg) − 148 × (weight kg ÷ height cm)²
**Hume formula**: - Men: (0.3281 × weight kg) + (0.3393 × height cm) − 29.5336 - Women: (0.2969 × weight kg) + (0.1714 × height cm) + 13.122
**From body fat percentage** (most accurate if body fat % is known): LBM = total weight × (1 − body fat percentage ÷ 100)
Applications: - **Katch-McArdle TDEE**: uses LBM instead of total weight for BMR calculation, producing more accurate results for people with above-average muscle mass or below-average body fat - **Protein target**: some evidence supports calculating protein needs based on LBM rather than total weight for individuals with high body fat percentages
Privacy: all calculations run in the browser. No health data is transmitted.
Frequently Asked Questions
- Lean body mass (LBM) is a better basis than total bodyweight for calculating protein needs and calorie requirements — particularly for people with above-average or below-average body fat percentages. A person weighing 100kg with 40% body fat has 60kg of lean mass. Calculating protein at 2.0g/kg of LBM (120g/day) is more appropriate than 2.0g/kg of total bodyweight (200g/day) for this individual. For TDEE calculation, the Katch-McArdle formula uses LBM directly: BMR = 370 + (21.6 × LBM in kg), producing more accurate results for high or low body fat individuals than height/weight-based formulas.
- Technically, lean body mass (LBM) includes a small amount of essential fat (approximately 3% of bodyweight in men, 8–12% in women) located in the bone marrow, brain, nerve tissue, and organs. Fat-free mass (FFM) excludes all fat. In practice, many sources use the terms interchangeably, and the difference is clinically insignificant for nutritional planning purposes. DEXA scan reports typically provide both fat mass and lean mass (which may or may not include essential fat depending on the software) — check your scan report's specific definitions.
- The most practical method for home tracking: use the US Navy circumference-based body fat estimate monthly and calculate LBM from (total weight × (1 − body fat %)). Track both total weight and LBM on the same graph. During a muscle-building phase, you want total weight increasing and LBM increasing — ideally LBM increasing faster than total weight. During a fat loss phase, you want total weight decreasing and LBM stable or declining only slightly (under 20% of total weight loss should come from lean mass to indicate good muscle preservation).
- Yes, but with important conditions. Body recomposition (simultaneous fat loss and muscle gain) occurs most readily in: beginners to resistance training (the 'newbie gains' period of 6–12 months); people returning after a training break (muscle memory effect); and individuals with high body fat (over 25% in men, 35% in women) who can fuel muscle synthesis from stored fat. For intermediate and advanced lifters, recomposition is much slower than dedicated bulk or cut phases. The conditions required: adequate protein (2.0–2.4g/kg), a small calorie deficit or maintenance calories, and consistent progressive overload resistance training.