Calculate Your Lean Body Mass
Track your muscle mass with precision FFMI analysis and muscle potential assessment
Enter Your Information
Quick Guide
LBM: Total weight minus fat mass
FFMI: Like BMI but for muscle mass
Good FFMI: Men 20-25, Women 17-21
Your Results
FFMI
Category
Muscle Mass
Estimated skeletal muscle
Body Fat
Current level
What This Means
Understanding LBM and FFMI
Lean Body Mass
Everything except fat tissue - muscle, bone, organs, and water. Tracking LBM shows true progress beyond scale weight.
FFMI Score
Fat-Free Mass Index shows how much muscle you carry relative to height. Men: 20-25 is good. Women: 17-21 is good.
Muscle Potential
Most people can gain 8-12kg muscle in year one, then 1-3kg annually. Track monthly for meaningful progress data.
How the Lean Body Mass Calculator Works
Understanding your muscle and tissue composition
The Boer Formula
LBM calculates total body weight minus fat mass. This includes muscle, bone, organs, and water. The Boer formula uses height and weight with gender-specific constants validated by MRI studies.
Lean mass determines metabolic rate. Muscle tissue burns 3x more calories than fat tissue at rest. Higher LBM means higher calorie needs and better metabolic health.
LBM Composition:
- • Skeletal muscle: 40-50% of LBM
- • Organs: 20-30% of LBM
- • Bone: 15-20% of LBM
- • Water: Distributed throughout
Why LBM Matters for Goals
LBM is the muscle you want to keep during fat loss or build during muscle gain. Track LBM to ensure your diet preserves muscle while losing fat, or confirms you're actually building muscle, not just gaining fat.
LBM Applications:
- • Protein needs: Calculate based on LBM (0.8-1g per lb)
- • Metabolic rate: More accurate TDEE estimation
- • Progress tracking: Separate fat loss from muscle loss
- • Goal setting: Realistic muscle gain targets
When to Use the Lean Body Mass Calculator
Tracking true body composition changes
During Fat Loss
Track LBM monthly to ensure you're losing fat, not muscle. LBM should stay stable or decline minimally (<2-3 lbs).
Building Muscle
Calculate LBM monthly to verify actual muscle gains. Realistic gain: 1-2 lbs LBM per month for beginners.
Body Recomposition
LBM tracks success better than scale. Stable weight with rising LBM means fat loss + muscle gain.
LBM Tracking Best Practices
Accurate LBM Tracking:
- • Measure body fat % accurately (Navy method/calipers)
- • Test monthly, same day/time each month
- • Track trend over 3+ months, not single tests
- • Use LBM for protein calculations (not total weight)
- • Expect 1-2 lbs LBM gain per month (beginners)
- • During cuts, LBM should stay mostly stable
LBM Tracking Errors:
- • Using bioimpedance scales (highly inaccurate)
- • Testing weekly (normal fluctuations mislead)
- • Expecting linear increases (progress plateaus)
- • Not accounting for water weight changes
- • Comparing tests at different hydration states
- • Unrealistic expectations (10+ lbs/month LBM gain)