Lean Body Mass Calculator - Muscle Mass Calculator
Calculate lean body mass, fat-free mass, and muscle percentage. Measure body composition with Boer, James, and Hume formulas for accurate lean mass calculation. Track muscle gain, fat loss, and body recomposition with our free LBM calculator for fitness and health goals.
Lean Body Mass by Different Formulas
Your Body Composition
Lean Body Mass Category
Muscle Building Goals
How Lean Body Mass Calculator Works
Calculate your muscle mass in 3 steps:
Enter Your Details
Input gender, age, weight, and height. Optional: add body fat % for most accurate calculation. All data processes using scientifically validated formulas.
Calculate with 3 Formulas
Uses Boer, James, and Hume formulas - medical standards for lean body mass calculation. If body fat % provided, uses direct calculation method.
View Body Composition
See lean mass, fat mass, muscle percentage, and category. Set muscle building goals and track progress over time for body recomposition.
Understanding Lean Body Mass & Formulas
Boer Formula (1984)
Most Popular- ✅ Most widely used in research
- ✅ Developed from multiple studies
- ✅ Accounts for gender differences
- ✅ Accurate for general population
James Formula (1976)
Conservative- ✅ Based on cadaver studies
- ✅ Conservative estimates
- ✅ Accounts for body proportions
- ✅ Used in clinical settings
Hume Formula (1966)
Clinical Standard- ✅ Clinical medicine standard
- ✅ Drug dosage calculations
- ✅ Validated in hospitals
- ✅ Reliable for medical use
Body Fat % Method
Most Accurate- ✅ Most accurate if BF% known
- ✅ Direct measurement
- ✅ Accounts for individual variation
- ✅ Used by fitness professionals
Note: All formulas give estimates ±2-3 kg. Body fat % method is most accurate but requires knowing your body fat percentage (from DEXA, bod pod, or calipers). Formulas are best for tracking changes over time.
LBM vs FFM vs Muscle Mass - What's the Difference?
Lean Body Mass (LBM)
Everything except essential fat: muscles, bones, organs, water, connective tissue. Includes 2-5% essential fat (men) or 10-13% (women) needed for survival. LBM = Total Weight - Storage Fat.
Fat-Free Mass (FFM)
EVERYTHING except ALL fat (including essential). Muscles, bones, organs, water minus all fat tissue. FFM = Total Weight - All Body Fat. Slightly lower than LBM by 2-13%.
Skeletal Muscle Mass
Only voluntary muscles you can control and train (biceps, quads, abs). Excludes heart, organs, bones. Typically 40-50% of LBM. This is what you build through weight training!
Example Breakdown (70kg person, 15% body fat):
Total Weight: 70 kg | Body Fat: 15% (10.5 kg)
LBM = 70 - 10.5 + 3.5 (essential fat) = 63 kg
FFM = 70 - 10.5 (all fat) = 59.5 kg
Skeletal Muscle = 63 × 0.45 = ~28 kg trainable muscle
Why Lean Body Mass Matters
Higher Metabolism
Muscle burns 3× more calories than fat at rest. 1kg muscle = 13 kcal/day vs 1kg fat = 4.5 kcal/day. More LBM = higher BMR = easier weight maintenance.
Strength & Performance
Higher LBM = stronger, more powerful, better athletic performance. Muscle generates force for movement, sports, daily activities. Essential for quality of life as you age.
Bone Density
Muscle pulls on bones during training, stimulating bone growth. High LBM protects against osteoporosis, fractures, bone loss with aging. Especially important for women post-menopause.
Disease Prevention
High LBM reduces risk of diabetes, heart disease, metabolic syndrome. Muscle improves insulin sensitivity, glucose metabolism. Sarcopenia (muscle loss) linked to mortality.
Aging Gracefully
Adults lose 3-8% muscle per decade after 30 if inactive. High LBM = independence, mobility, strength into old age. Resistance training preserves LBM regardless of age.
Better Body Composition
Scale weight lies! 70kg at 60kg LBM (lean) looks completely different than 70kg at 50kg LBM (high fat). Focus on building LBM, not just losing weight.
How to Increase Lean Body Mass
Progressive Overload
Lift heavy weights 3-5×/week. Focus on compound movements: squats, deadlifts, bench, rows. Increase weight/reps progressively. Muscle grows in response to mechanical tension and progressive challenge.
High Protein Intake
Eat 1.6-2.2g protein per kg body weight daily. Muscle needs amino acids to grow and repair. Distribute across 4-5 meals. Prioritize lean meats, fish, eggs, dairy, legumes, protein powder.
Calorie Surplus (Lean Bulk)
Eat 200-300 kcal above TDEE for muscle gain. Gain 0.25-0.5kg per week maximum. Faster = more fat gain. Track calories, protein, adjust weekly based on results.
Sleep 7-9 Hours
Muscle grows during sleep, not training! Growth hormone peaks during deep sleep. Poor sleep = higher cortisol, less testosterone, muscle breakdown. Sleep = recovery = growth.
Creatine Supplementation
5g creatine monohydrate daily increases muscle mass 1-2kg in 8 weeks. Improves strength, power, workout performance. Most researched, safest muscle building supplement. Cheap and effective.
Track Progress
Measure LBM monthly, not weekly. Take photos, track strength (lift progression). Scale weight can mislead during recomp (losing fat + gaining muscle). Focus on LBM trend over 3-6 months.
Why Use Our LBM Calculator?
3 Scientific Formulas
Uses Boer, James, and Hume formulas - all medically validated. Averages results for most accurate lean mass estimate. Plus body fat % method if known.
Complete Body Composition
See lean mass, fat mass, muscle percentage, and category. Visual chart shows exact body composition breakdown. Know exactly what you're made of!
Muscle Building Goals
Calculate target LBM for +5kg, +10kg muscle gain. See elite-level muscle mass potential (FFMI 25). Set realistic goals based on your height and frame.
LBM Categories
Know if you have low, average, above average, or athletic muscle mass for your height. Compare yourself to population standards. Track improvement over time.
Metric & Imperial Units
Switch between kg/cm and lbs/inches instantly. Perfect for global users from USA, UK, Europe, Asia, Australia. Universal fitness tracking.
Mobile Friendly
Calculate LBM on any device. Track muscle gain at gym, home, or anywhere. Free, no signup required. Instant results!
Frequently Asked Questions
What is lean body mass (LBM)?
Lean Body Mass (LBM) is total body weight minus storage fat, including muscles, bones, organs, water, and essential fat needed for survival (2-5% men, 10-13% women). LBM represents your "metabolically active" tissue. Example: 70kg person with 15% body fat has ~60kg LBM. Higher LBM = higher metabolism, more strength.
How accurate are LBM calculators?
LBM formulas (Boer, James, Hume) are accurate ±2-3 kg for most people. Body fat % method is most accurate (±1 kg) if you know your true body fat percentage from DEXA, bod pod, or hydrostatic weighing. Use calculator for tracking changes over time, not absolute numbers. Monthly measurements show muscle gain/loss trends reliably.
What's the difference between LBM and FFM?
LBM (Lean Body Mass) = Total Weight - Storage Fat (includes essential fat). FFM (Fat-Free Mass) = Total Weight - ALL Fat (no essential fat). LBM is slightly higher than FFM. Example: 70kg man, 15% body fat: LBM = 63kg (includes 3kg essential fat), FFM = 60kg (zero fat). Both track muscle gain equally well.
How much muscle can I gain naturally?
Beginners: 1-1.5kg muscle per month (year 1). Intermediate: 0.5-1kg per month (year 2). Advanced: 0.25-0.5kg per month (year 3+). Genetic limit: FFMI (Fat-Free Mass Index) of 25 for natural lifters. Women gain at 50-60% of male rates. Requires progressive overload, high protein (1.6-2.2g/kg), calorie surplus, consistency.
Can I gain muscle and lose fat simultaneously?
Yes, but only for: beginners (training <1 year), those returning after break, or obese individuals. Called "body recomposition." Requires: slight calorie deficit (TDEE -200 to -300), high protein (2g/kg), progressive strength training 4×/week. LBM stays same or increases slightly while fat mass drops. Advanced lifters must choose: bulk or cut.
Does LBM decrease with age?
Yes, sarcopenia (muscle loss) starts at 30. Sedentary adults lose 3-8% muscle per decade. By 80, can lose 40-50% of peak muscle mass! Solution: resistance training 2-3×/week maintains LBM at any age. Adults who lift weights have same LBM at 70 as sedentary 30-year-olds. Never too late to start!
What's a good LBM for my height?
Varies by gender and height. Men: Low <60kg, Average 60-70kg, Above Average 70-80kg, Athletic >80kg (for 175cm height). Women: Low <45kg, Average 45-55kg, Above Average 55-65kg, Athletic >65kg (for 165cm height). Calculate FFMI (FFM / height² in meters) - 18-20 is average, 22-24 is athletic, 25+ is elite natural lifter.
Why does my scale weight stay same but I look leaner?
Body recomposition! Losing fat while gaining muscle simultaneously. Example: Lost 3kg fat + gained 3kg muscle = same scale weight but completely different body composition. This is why LBM matters more than weight! Focus on: measurements, photos, how clothes fit, strength gains, body fat %, LBM changes. Scale weight alone is meaningless.