Lean Body Mass (LBM) Calculator
Enter your weight and body fat percentage to calculate your lean body mass (LBM) and fat mass. Set a target body fat percentage to simulate the weight you would reach while keeping your lean mass unchanged.
Tips
- Lean body mass (LBM) is the total weight of everything in your body except fat — muscle, bone, organs, and body water. It is commonly used as a goal to preserve while cutting fat.
- Enter a body fat percentage measured with a body composition scale or skinfold calipers. Different measurement methods can vary by several percentage points.
- Set a lower target than your current body fat to see your weight after fat loss, or a higher target to see your weight after a bulking phase.
- Tracking body fat percentage alongside weight makes it much easier to see how training and diet are changing your body composition over time.
FAQ
Side Note — How measuring body fat has evolved
Estimating body fat percentage has a long history. In the early 20th century, hydrostatic weighing — based on Archimedes' principle — was considered the "gold standard." A person was fully submerged in a water tank so their body volume could be measured, and body fat percentage was calculated from the density difference between fat tissue and lean tissue. It was highly accurate but required bulky, specialized equipment.
Since the 1990s, bioelectrical impedance analysis (BIA), now built into many home body composition scales, has become the dominant everyday method. A weak electrical current is passed through the body, and body fat percentage is estimated from how easily the current flows (impedance) — fat tissue contains little water and resists current, while muscle and blood are water-rich and conduct more easily. It is convenient, but sensitive to your body's hydration level at the time of measurement (meals, fluids, recent exercise), so measuring at a consistent time and under consistent conditions is recommended.
In strength training circles, two phases are often discussed: "cutting," which aims to lose fat while preserving as much lean body mass as possible, and "bulking," which aims to increase lean body mass (mainly muscle). Tracking the breakdown between lean mass and fat mass — not just total body weight — makes it much easier to tell whether your body is actually changing in the direction you intend.