Lean Body Mass Calculator
Enter your height, weight, and sex to calculate your lean body mass — the weight of muscle, bone, organs, and water, excluding fat.
What Is Lean Body Mass?
Lean body mass (LBM) is the total weight of your body minus your body fat. It includes muscle, bone, organs, connective tissue, and the water stored within them. For a 75 kg person with 20% body fat, LBM = 75 × (1 − 0.20) = 60 kg.
LBM matters because it is the metabolically active component of body weight. Your basal metabolic rate (BMR) is driven almost entirely by lean mass — fat tissue burns very few calories at rest. Knowing your LBM enables more accurate protein targets (typically 1.6–2.2 g per kg of LBM for athletes), better drug dosing in clinical settings, and more meaningful tracking of body composition changes over time.
This calculator estimates LBM using three formulas — Boer, James, and Hume — that rely on height, weight, and sex. If you already know your body fat percentage, you can calculate a more accurate LBM directly: LBM = total weight × (1 − body fat %).
The Three Formulas
All three formulas use height (cm) and weight (kg). Results are in kg.
| Formula | Male | Female |
|---|---|---|
| Boer (1984) | 0.407 × weight + 0.267 × height − 19.2 | 0.252 × weight + 0.473 × height − 48.3 |
| James (1976) | 1.1 × weight − 128 × (weight/height)² | 1.07 × weight − 148 × (weight/height)² |
| Hume (1966) | 0.3281 × weight + 0.33929 × height − 29.5336 | 0.29569 × weight + 0.41813 × height − 43.2933 |
Worked Examples
Example 1: Male, 180 cm, 80 kg. Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg. James: 1.1 × 80 − 128 × (80/180)² = 88 − 128 × 0.198 = 88 − 25.3 = 62.7 kg. Hume: 0.3281 × 80 + 0.33929 × 180 − 29.5336 = 57.7 kg. Average ≈ 60.6 kg.
Example 2: Female, 165 cm, 62 kg. Boer: 0.252 × 62 + 0.473 × 165 − 48.3 = 15.6 + 78.0 − 48.3 = 45.4 kg. James: 1.07 × 62 − 148 × (62/165)² = 66.3 − 148 × 0.141 = 66.3 − 20.9 = 45.5 kg. Hume: 0.29569 × 62 + 0.41813 × 165 − 43.2933 = 42.8 kg. Average ≈ 44.6 kg.
Example 3: Male, 175 cm, 95 kg (likely higher body fat). Boer: 0.407 × 95 + 0.267 × 175 − 19.2 = 38.7 + 46.7 − 19.2 = 66.2 kg. This means approximately 29 kg of fat mass, or ~30% body fat — consistent with a higher-weight individual.
Frequently Asked Questions
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There is no universal "ideal" LBM — it depends on height, sex, and goals. A rough benchmark: men often have LBM in the range of 60–80% of total body weight, women 55–75%. Athletes typically sit at the higher end. More useful than a raw number is tracking LBM over time to ensure muscle is being preserved or gained.
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Lean body mass includes muscle but also bone, organs, blood, and body water. Skeletal muscle typically accounts for about 40–50% of LBM in healthy adults. Muscle mass can be estimated more precisely with DEXA scanning or bioelectrical impedance analysis (BIA).
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Research generally recommends 1.6–2.2 g of protein per kg of LBM per day for people looking to build or preserve muscle. For example, someone with 60 kg LBM should aim for 96–132 g of protein per day. Using LBM rather than total body weight avoids over-prescribing protein for people with high body fat.
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Yes. Resistance training is the primary driver of lean mass gain. Progressive overload — gradually increasing training stress — stimulates muscle protein synthesis. Adequate protein intake (1.6–2.2 g/kg LBM) and a slight calorie surplus support muscle growth. Gains slow significantly after the first few years of training.
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Each formula was derived from a different population sample using different measurement methods. Boer used underwater weighing; James used total body water; Hume used isotope dilution. The populations differed in age, ethnicity, and fitness level. No formula is perfectly accurate for all individuals — the average across all three is a more robust estimate.
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Almost. Fat-free mass (FFM) excludes all fat, including essential fat in the brain, nerves, and cell membranes. LBM includes a small amount of essential fat (roughly 2–5% of body weight). In everyday usage the terms are often used interchangeably, and the difference is small enough to be negligible for most purposes.