How Lean Body Mass is calculated
Three validated formulas are used and averaged:
| Formula | Men | Women |
|---|---|---|
| Boer (1984) | 0.407W + 0.267H − 19.2 | 0.252W + 0.473H − 48.3 |
| James (1976) | 1.1W − 128(W/H)² | 1.07W − 148(W/H)² |
| Hume (1966) | 0.3281W + 0.33929H − 29.5 | 0.29569W + 0.41813H − 43.3 |
W = weight in kg, H = height in cm. If you know your body fat percentage, entering it gives the most accurate lean mass calculation.
How to use your results
Lean body mass is used to calculate protein targets (1.6–2.2g per kg lean mass for athletes), to track body composition changes, and for more accurate TDEE estimation.
Tracking lean mass over time shows whether you're gaining muscle or losing it — more useful than scale weight alone, which changes with water retention and fat simultaneously.
Frequently asked questions
What is lean body mass?
Lean body mass (LBM) is your total body weight minus fat mass. It includes muscle, bone, water, organs and connective tissue. It's also called fat-free mass (FFM).
How do I increase lean body mass?
Progressive resistance training (weightlifting) is the primary way to increase muscle tissue, which is the main component of LBM. Adequate protein (1.6–2.2g/kg LBM) and slight calorie surplus support muscle growth.
What is a healthy lean body mass?
LBM varies significantly by height and sex. A useful reference: for a 175cm man at 15% body fat, LBM ≈ 68 kg. For a 165cm woman at 25% body fat, LBM ≈ 56 kg. Track change over time rather than absolute numbers.
How accurate are lean body mass formulas?
Formula accuracy is ±3–5 kg compared to DEXA scanning. The formulas are most accurate for people with average body composition. Very muscular or very obese individuals may see larger discrepancies.
Why does lean body mass matter for protein intake?
Protein recommendations are often given per kg of lean body mass rather than total body weight — particularly for people with high body fat. 2.0g protein per kg LBM is more appropriate than 2.0g per kg total weight for an obese person.
Can I gain lean mass while losing fat?
Yes — 'body recomposition' is possible, particularly for beginners, people returning after a break, and those with significant fat to lose. It requires adequate protein (2.0g/kg LBM), resistance training, and maintenance calories.
What is the difference between lean mass and muscle mass?
Lean mass includes all non-fat tissue: muscle, bone, organs, skin, and water. Muscle mass is only the skeletal muscle component — typically 35–45% of lean mass. MRI or ultrasound are needed to measure muscle mass specifically.
How fast can I gain lean body mass?
Natural muscle gain is approximately 0.5–1 kg per month for beginners, 0.25–0.5 kg for intermediate lifters, and 0.1–0.25 kg for advanced. These are upper bounds — most people gain less due to training and nutrition inconsistencies.