Lean Body Mass Calculator
Estimate lean body mass using Boer, James and Hume formulas.
Inputs
Average LBM (all formulas)
57.2kg
Boer (1984)
58.1kg
James (1976)
59.0kg
Hume (1966)
54.4kg
Estimated Fat Mass (Boer basis)
17.0kg
Estimated Body Fat %
22.6%
Derived from Boer LBM; use the Body Fat Calculator for a tape-measure estimate.
Step by step
Input (metric)
= 75 kg, 175 cm, male
Boer LBM
0.407 × 75 + 0.267 × 175 − 19.2
= 58.1 kg
James LBM
1.1 × 75 − 128 × (75/175)²
= 59 kg
Hume LBM
0.3281 × 75 + 0.33929 × 175 − 29.5336
= 54.4 kg
How it works
Lean Body Mass (LBM) is total body weight minus fat mass. It includes muscle, bone, water, and organs. Unlike total weight, LBM is directly tied to metabolic rate, drug dosing, and protein requirements. Three established formulas are shown because each was validated in a different clinical context — comparing them reveals the degree of uncertainty in any single prediction.
Formulas
Boer (1984) — male
LBM = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2
- W
- Weight in kg
- H
- Height in cm
Boer (1984) — female
LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3
- W
- Weight in kg
- H
- Height in cm
James (1976) — male
LBM = 1.1 × weight − 128 × (weight/height)²
- W
- Weight in kg
- H
- Height in cm
Hume (1966) — male
LBM = 0.3281 × weight + 0.33929 × height − 29.5336
- W
- Weight in kg
- H
- Height in cm
LBM estimates from height and weight carry ±3–5 kg error compared to DEXA scanning. This tool is for informational purposes only and is not a substitute for clinical body composition assessment.
Frequently Asked Questions
Why do the three formulas give different results?
Each formula was derived from a different population and era. Boer (1984) is based on bioelectrical impedance in European subjects; James (1976) on UK data; Hume (1966) on a small Canadian cohort. No single equation is universally superior, so the average across all three is the most robust single figure to use.
What is LBM used for in medicine?
LBM is used to calculate drug doses (especially chemotherapy and antibiotics), GFR (kidney function), and target weights for ICU nutritional support. Total body weight would overdose larger individuals; LBM-adjusted dosing is more accurate and safer.
How does LBM differ from fat-free mass?
Fat-free mass (FFM) and LBM are often used interchangeably, but strictly speaking LBM includes essential fat in the nervous system, bone marrow and organs (~3% for men, ~8–12% for women). FFM is zero fat. In practice the difference is small enough that most clinical references treat them as equivalent.