Calculate your lean body mass.
Lean Body Mass (LBM) is everything in your body except fat: muscles, bones, organs, water. It's crucial for calculating your protein needs, calorie expenditure, and assessing your body composition progress.
LBM = Body Weight × (1 - Body Fat % / 100)
Example: 180 lbs at 20% body fat
→ LBM = 180 × (1 - 0.20) = 180 × 0.80 = 144 lbs lean mass
This means:
• 144 lbs of muscle, bone, organs, water
• 36 lbs of body fat
Men (at 180 lbs):
• 10% BF: 162 lbs LBM (Athlete)
• 15% BF: 153 lbs LBM (Fit)
• 20% BF: 144 lbs LBM (Average)
• 25% BF: 135 lbs LBM
Women (at 140 lbs):
• 18% BF: 115 lbs LBM (Fit)
• 25% BF: 105 lbs LBM (Average)
• 30% BF: 98 lbs LBM
LBM determines your basal metabolic rate – more lean mass = higher calorie burn. It's also the basis for protein calculations (0.7-1g per lb LBM) and shows your actual fitness progress beyond the scale.
The recommendation is 0.7-1g protein per pound of lean body mass. At 144 lbs LBM: 100-144g protein daily. This calculation is more accurate than protein per total body weight, especially at higher body fat percentages.
Yes, especially as a beginner! This is called "Body Recomposition." With adequate protein and resistance training, you can build muscle while losing fat – weight stays the same but body composition improves.
LBM (Lean Body Mass) and FFM (Fat-Free Mass) are often used interchangeably. Technically, LBM includes a small amount of essential fat (nerves, cell membranes), FFM includes no fat at all. In practice, the difference is negligible.
Pro Tip: During a diet, LBM should stay as stable as possible! If your lean mass is dropping, you're losing muscle – increase protein intake and reduce calorie deficit.