All calculatorsLean Body Mass (LBM) Calculator
Estimate lean body mass (LBM) in kilograms (and percent) using body-fat % or classic formulae (Boer, James, Hume). Clear steps, a composition bar, and a lean-mass gauge.
Background
LBM is body weight minus fat mass. If body-fat percentage is known: LBM = Weight × (1 − BF%/100). When % is unavailable, empirical models (Boer, James, Hume) estimate LBM from weight and height with sex-specific coefficients.
How this calculator works
- Body-fat route: If %BF is known, LBM = Weight × (1 − %BF/100).
- Boer (1984): Male: LBM = 0.407·W + 0.267·H − 19.2; Female: LBM = 0.252·W + 0.473·H − 48.3 (W in kg, H in cm).
- James (1976): Male: LBM = 1.1·W − 128·(W²/H²); Female: LBM = 1.07·W − 148·(W²/H²).
- Hume (1966): Male: LBM = 0.32810·W + 0.33929·H − 29.5336; Female: LBM = 0.29569·W + 0.41813·H − 43.2933.
- Outputs: We return LBM (kg), fat mass (kg), and LBM%.
Formula & Equation Used
From body-fat %: LBM = W × (1 − BF%/100)
Boer (1984): Male LBM = 0.407W + 0.267H − 19.2; Female LBM = 0.252W + 0.473H − 48.3
James (1976): Male LBM = 1.1W − 128(W²/H²); Female LBM = 1.07W − 148(W²/H²)
Hume (1966): Male LBM = 0.32810W + 0.33929H − 29.5336; Female LBM = 0.29569W + 0.41813H − 43.2933
Example Problem & Step-by-Step Solution
Example 1 — 75 kg, 178 cm, 18% BF (Male)
LBM = 75 × (1 − 0.18) = 61.5 kg; Fat mass = 13.5 kg; LBM% = 82%.
Example 2 — Male 190 lb, 70 in (Boer)
Convert: 190 lb → 86.18 kg; 70 in → 177.80 cm.
Boer (male): LBM = 0.407·W + 0.267·H − 19.2
= 0.407·86.18 + 0.267·177.80 − 19.2
= 35.08 + 47.53 − 19.20 = 63.35 kg.
Fat mass = 86.18 − 63.35 = 22.83 kg.
LBM% = (63.35 / 86.18) × 100 ≈ 73.51%.
Example 3 — Female 140 lb, 64 in (Hume)
Convert: 140 lb → 63.50 kg; 64 in → 162.56 cm.
Hume (female): LBM = 0.29569·W + 0.41813·H − 43.2933
= 0.29569·63.50 + 0.41813·162.56 − 43.2933
= 18.77 + 67.97 − 43.29 = 43.46 kg.
Fat mass = 63.50 − 43.46 = 20.05 kg.
LBM% = (43.46 / 63.50) × 100 ≈ 68.43%.
Frequently Asked Questions
Q: Which method should I choose?
If you have a reliable body-fat %, use it. Otherwise, Boer is widely used clinically; James and Hume are older but still common.
Q: What units do I enter?
Enter weight in kg or lb, height in cm or in. We convert internally to kg and cm.
Q: Is LBM the same as fat-free mass?
They’re often used interchangeably; small definitional differences exist in research contexts.
