How to Calculate Lean Body Mass
What is Lean Body Mass?
Lean Body Mass (LBM) is total body weight minus fat mass. It includes muscle, bone, organs, and water. Used in clinical dosing, fitness tracking, and metabolic rate estimation.
Formula
LBM (kg) = Weight × (1 − body_fat%/100); LBM (men) = 1.1 × weight − 4.8 × height (simplified)
- BW
- Body weight (kg)
- %BF
- Body fat percentage (%)
- LBM
- Lean Body Mass (kg)
Step-by-Step Guide
- 1LBM = Total weight × (1 − body fat fraction)
- 2Boer formula (men): LBM = 0.407×W + 0.267×H − 19.2
- 3Boer formula (women): LBM = 0.252×W + 0.473×H − 48.3
- 4James formula alternative: LBM(men) = 1.1×W − 128×(W/H)²
Worked Examples
Input
80kg total, 20% body fat
Result
LBM = 80 × (1−0.20) = 64 kg lean mass
Frequently Asked Questions
What is lean body mass?
Everything except fat: muscle, bone, water, organs. More useful than total weight for athletic performance.
Why is LBM important?
Determines calories for maintenance, strength capacity, metabolic rate. Athletes focus on LBM, not total weight.
Can LBM increase without weight gain?
Yes—if muscle increases and fat decreases (same weight). Requires resistance training and good nutrition.