Lean Body Mass Calculator
Calculate your lean body mass using Boer, James, and Hume formulas. Compare results across methods and understand your body composition.
Lean Body Mass is your total weight minus body fat. For most adults, LBM is 60-90% of total body weight depending on fitness level.
Calculate your exact LBM using three scientific formulas below.
Your Measurements
What Is Lean Body Mass and Why Should You Care?
Lean body mass is everything in your body that isn't stored fat: muscles, bones, organs, water, skin, and connective tissue. It's the metabolically active part of you — the part that burns calories, moves your body, and keeps you alive.
Two people can weigh exactly the same but have completely different body compositions. A 75 kg person with 60 kg of lean mass and 15 kg of fat looks, performs, and ages differently from someone at 75 kg with 50 kg of lean mass and 25 kg of fat. The scale doesn't tell you this. LBM does.
LBM also drives your metabolism. Every kilogram of muscle burns roughly 13 calories per day at rest, while fat burns only 4.5. This is why two people of the same weight can have very different calorie needs — the one with more lean mass burns more, even sitting on the sofa.
The Three Formulas Compared
| Formula | Year | Inputs | Best For |
|---|---|---|---|
| Boer | 1984 | Weight, height, sex | Most accurate for adults (validated with DEXA) |
| James | 1976 | Weight, height, sex | Classic formula, widely cited in research |
| Hume | 1966 | Weight, height, sex | Oldest, still used in clinical settings |
What this means for you: All three formulas give estimates — none are as accurate as a DEXA scan or hydrostatic weighing. This calculator shows all three and averages them, which tends to reduce individual formula error. If the three results differ by more than 3–4 kg, your body proportions may be unusual for the population the formulas were designed for.
Typical LBM Ranges
| Category | Men (LBM % of body weight) | Women (LBM % of body weight) |
|---|---|---|
| Athletes | 85–92% | 78–85% |
| Fit adults | 80–88% | 72–80% |
| Average adults | 72–82% | 65–75% |
| Overfat | < 72% | < 65% |
Women naturally carry more essential body fat (10–13% vs 2–5% for men), so their LBM percentage is always lower at the same fitness level. This isn't a health concern — it's biology.
How to Increase Lean Body Mass
Resistance Training
Train each muscle group 2x per week with progressive overload. Compound movements (squats, deadlifts, bench press, rows) build the most lean mass per minute of training. Use our One Rep Max Calculator to set training weights.
Adequate Protein
Consume 1.6–2.2g protein per kg of body weight daily. Spread across 3–5 meals for maximum muscle protein synthesis. Check your needs with our Protein Calculator.
Calorie Surplus (for gain)
Building muscle requires energy. A surplus of 200–300 calories above your TDEE supports lean mass gain while minimising fat gain. Find your TDEE with our TDEE Calculator.
Sleep and Recovery
Growth hormone — critical for muscle repair — is released primarily during deep sleep. Aim for 7–9 hours. Poor sleep reduces muscle protein synthesis by up to 18%. Use our Sleep Calculator to time your cycles.
Related Body Composition Tools
How to use this tool
Select your preferred unit system (Imperial or Metric)
Enter your age and select your gender
Input your height
Common uses
- Tracking muscle mass changes during training
- Calculating more accurate calorie needs
- Monitoring body composition over time
- Comparing body composition across formulas
- Setting muscle-building targets
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