Muscle Mass Calculator - Calculate Your Lean Body Mass
Calculate your muscle mass, lean body mass, and body composition. Track your muscle building progress with accurate measurements.
Your Muscle Mass
Lean Body Mass
0.0 lbs
Muscle Mass Percentage
Body Composition Breakdown
Your FFMI Score
Fat-Free Mass Index - measures muscle mass relative to height
Enter Your Information
We calculate your muscle mass using the Deurenberg formula for body fat percentage, combined with FFMI methodology.
What is Lean Body Mass?
Lean Body Mass (LBM), also called Fat-Free Mass, is your total body weight minus all fat tissue. It includes muscles, bones, organs, skin, blood, and water—everything except stored body fat.
For most fitness enthusiasts, lean body mass is primarily about skeletal muscle—the muscle you can grow through resistance training. While you cannot change your bone or organ mass significantly, you can dramatically increase your muscle mass through proper training and nutrition.
Components of Lean Body Mass
Skeletal Muscle (~40-50%)
The muscles attached to bones that you train in the gym. This is what grows with resistance training.
Bone Mass (~15%)
Your skeleton. Weight-bearing exercise can increase bone density but not significantly change mass.
Organs (~10-15%)
Heart, liver, kidneys, brain, and other vital organs. Relatively constant in adults.
Body Water (~20-25%)
Water in muscles, blood, and tissues. Can fluctuate daily based on hydration and diet.
Why Muscle Mass Matters
Metabolic Health
Muscle is metabolically active tissue. More muscle means higher basal metabolic rate (BMR), making it easier to maintain a healthy weight and body composition.
Functional Strength
Greater muscle mass translates to improved strength for daily activities, sports performance, and injury prevention.
Body Composition
Higher lean mass relative to fat mass creates the "toned" or athletic look most people desire, regardless of scale weight.
Longevity
Research shows that maintaining muscle mass as you age is associated with better mobility, independence, and overall health outcomes.
How to Build Muscle Mass
1. Progressive Resistance Training
Lift weights that challenge you. Progressively increase weight, reps, or sets over time. Train each muscle group 2-3 times per week for optimal growth. Focus on compound exercises (squats, deadlifts, bench press, rows) supplemented with isolation work.
2. Adequate Protein Intake
Consume 1.6-2.2 grams of protein per kilogram of body weight daily. Spread protein intake across 4-5 meals for optimal muscle protein synthesis. Quality sources include lean meats, fish, eggs, dairy, and legumes.
3. Caloric Surplus
To build muscle, you typically need to eat more calories than you burn. A surplus of 200-500 calories above your TDEE is recommended. Too large a surplus leads to excessive fat gain alongside muscle.
4. Recovery and Sleep
Muscles grow during rest, not in the gym. Aim for 7-9 hours of quality sleep per night. Allow 48-72 hours between training the same muscle group. Manage stress, as high cortisol impairs muscle growth.
Realistic Muscle Gain Expectations
Muscle building is a slow process. Here are research-backed expectations for natural lifters:
| Training Experience | Monthly Gain (Men) | Monthly Gain (Women) |
|---|---|---|
| Beginner (0-1 years) | 1-1.5 kg / 2-3 lbs | 0.5-0.75 kg / 1-1.5 lbs |
| Intermediate (1-3 years) | 0.5-1 kg / 1-2 lbs | 0.25-0.5 kg / 0.5-1 lb |
| Advanced (3+ years) | 0.25-0.5 kg / 0.5-1 lb | 0.1-0.25 kg / 0.25-0.5 lb |
These are averages under optimal conditions (training, nutrition, sleep). Individual results vary based on genetics, age, and consistency.
Frequently Asked Questions
Is lean body mass the same as muscle mass?
Not exactly. Lean body mass includes all non-fat tissue: muscles, bones, organs, and water. Muscle mass is a component of lean body mass. When people talk about "gaining lean mass," they usually mean gaining muscle specifically.
How accurate is this calculator without knowing my exact body fat?
This calculator estimates body fat using the Deurenberg formula based on your BMI, age, and gender. While useful for general guidance, it may be less accurate for athletes or those with unusual body compositions. For precise measurements, consider DEXA scans or hydrostatic weighing.
Can I lose fat and gain muscle at the same time?
Yes, this is called "body recomposition." It is most effective for beginners, those returning after a break, or people with higher body fat. However, the process is slower than focusing on one goal at a time. Eating at maintenance calories with high protein can facilitate recomposition.
What is a good lean body mass for my height?
This varies significantly by gender, age, and training history. As a rough guide for trained men: aim for FFMI of 20-22 as a solid intermediate goal, and 22-25 as advanced. For women, FFMI of 17-19 is above average. Use our FFMI calculator for a height-normalized comparison.
Does body type (somatotype) affect muscle building?
The ectomorph/mesomorph/endomorph classification is somewhat outdated, but it can reflect tendencies. "Ectomorphs" may need more calories and struggle to gain weight. "Endomorphs" may gain weight easily but also more fat. However, everyone can build significant muscle with proper training and nutrition—genetics influence rate and ceiling, not the ability to improve.
Medical Disclaimer
This calculator provides estimates for educational purposes only. Body fat estimation formulas have inherent limitations and may not be accurate for all individuals. Consult with healthcare professionals or certified fitness trainers for personalized advice. Do not make significant dietary or exercise changes without professional guidance.