Lean Body Mass Calculator
Calculate your lean body mass (total weight minus body fat).
What is Lean Body Mass (LBM)?
Lean Body Mass (LBM) is your total body weight minus all fat weight. It includes muscle, bone, organs, water, and connective tissue — everything that is not stored fat. LBM = Total Weight × (1 − Body Fat %).
For a 80 kg person with 20% body fat: LBM = 80 × (1 − 0.20) = 64 kg of lean mass. Tracking LBM alongside total weight helps distinguish between fat loss and muscle loss during a diet.
Why LBM Matters
LBM is a better indicator of metabolic health than total weight. More lean mass means higher BMR (you burn more calories at rest), better insulin sensitivity, stronger bones, and improved physical performance.
During weight loss, the goal should be to preserve LBM while reducing fat. Losing muscle along with fat (common with extreme caloric restriction or no resistance training) leads to a lower metabolism and a higher chance of weight regain.
Estimating LBM Without Body Fat Measurement
Several formulas estimate LBM from height, weight, and gender without requiring body fat measurement:
- Boer formula: Men: LBM = 0.407W + 0.267H − 19.2. Women: LBM = 0.252W + 0.473H − 48.3 (W in kg, H in cm)
- James formula and Hume formula offer similar estimates
These are estimates — for precise LBM, you need a body fat measurement via DEXA scan, hydrostatic weighing, or reliable body fat calipers.
Frequently Asked Questions
How much lean body mass should I have?
There is no universal target. Average LBM: men 60–80% of total weight, women 50–70%. Athletes and bodybuilders can have LBM above 85% (men) or 75% (women). Focus on the trend — maintaining or increasing LBM during fat loss is the goal.
Can I gain lean mass while losing fat?
Yes, especially if you are new to strength training, returning after a break, or have higher body fat. This is called body recomposition. Requires adequate protein (1.6–2.2g/kg), consistent resistance training, and a moderate caloric deficit (not extreme).
What is the difference between LBM and fat-free mass?
They are often used interchangeably, but technically LBM includes essential fat (3–5% in men, 10–13% in women) that is necessary for organ function. Fat-free mass excludes all fat. In practice the difference is small.