Lean Body Mass Calculator
Estimate your lean body mass (LBM) using three validated formulas: Boer, James, and Hume. Compare results and understand what lean mass means for your health.
📊 Average Lean Body Mass (All Methods)
Formula Comparison
| Formula | LBM Result | Est. Body Fat % |
|---|---|---|
| Boer Formula | -- | -- |
| James Formula | -- | -- |
| Hume Formula | -- | -- |
Understanding Lean Body Mass
Lean Body Mass (LBM) is your total body weight minus fat mass. It includes muscles, bones, organs, skin, blood, and water—essentially everything except stored fat.
💡 LBM vs Fat-Free Mass (FFM)
These terms are often used interchangeably, but technically LBM includes essential fat (about 3% for men, 12% for women) while FFM is purely non-fat tissue. For practical purposes, the difference is usually negligible.
The Formulas
Boer: LBM = (0.407 × 80) + (0.267 × 175) − 19.2 = 32.56 + 46.73 − 19.2 = 60.1 kg
James: LBM = 1.1 × 80 − 128 × (80/175)² = 88 − 128 × 0.209 = 88 − 26.75 = 61.25 kg
Hume: LBM = (0.32810 × 80) + (0.33929 × 175) − 29.5339 = 26.25 + 59.38 − 29.53 = 56.1 kg
Average LBM ≈ 59.2 kg (74% of body weight, implying ~26% body fat)
⚠️ Accuracy & Limitations
- Estimation only: These formulas provide rough estimates, not precise measurements
- Population bias: Formulas were developed primarily from Western populations
- No body comp data: They don't use actual body fat measurements
- Athletic variation: Athletes may have higher LBM than estimated
- Age factors: Muscle mass naturally decreases with age, which formulas don't account for
- Hydration: Body water affects actual lean mass but not these calculations
Why LBM Matters
Clinical Applications
LBM is used for drug dosing calculations, nutritional assessment, and monitoring muscle loss (sarcopenia) in aging populations. Higher LBM relative to total weight generally indicates better metabolic health.
Frequently Asked Questions
Lean body mass (LBM) is your total body weight minus fat mass. It includes muscle, bone, organs, skin, and water—everything except stored body fat.
All three formulas provide estimates with similar accuracy. The Boer formula is often considered well-balanced. However, none compares to direct measurement methods like DEXA or underwater weighing.
Technically, LBM includes essential fat (3% men, 12% women) while fat-free mass (FFM) excludes all fat. In practice, the terms are often used interchangeably.
Yes, through resistance training and adequate protein intake. Building muscle increases LBM. However, some components (bone, organs) don't change significantly in adults.
Each formula was developed from different study populations using different methodologies. The variation shows the inherent uncertainty in estimation-based approaches.
LBM helps with drug dosing (many drugs distribute through lean tissue), nutritional assessment, and tracking conditions like sarcopenia (age-related muscle loss).
Generally, higher LBM relative to fat mass indicates better metabolic health. However, extremely high LBM (as in some bodybuilders) may stress the heart. Context matters.
Muscle mass naturally decreases after about age 30 (sarcopenia). Without strength training, people lose 3-5% of muscle mass per decade. These formulas don't adjust for age.
No, these formulas are validated for adults only. Children's body composition changes rapidly during growth and requires age-specific assessments.
Lean mass is metabolically active and drives basal metabolic rate (BMR). More muscle means higher calorie burn at rest. This is why LBM is important in weight management.
For healthy adults: men typically have 75-85% LBM (15-25% body fat); women typically have 65-75% LBM (25-35% body fat). Athletes may have higher LBM percentages.
No, these formulas were primarily developed using Caucasian populations. Body composition varies across ethnicities, so results may be less accurate for diverse populations.