Lean Body Mass Calculator
Lean body mass is your total weight minus fat - muscles, bones, organs, water. Knowing it helps you set protein targets, track muscle gains, and calculate more accurate calorie needs. This gives you the number from three different formulas.
How to use
- Select your gender.
- Pick your units and enter your weight and height.
- Hit Calculate to see your LBM from three different methods.
- The three formulas usually give similar results. The average is a solid estimate to work with.
Related tools:
Lean body mass (LBM) is your total weight minus body fat - essentially everything that is not fat: muscle, bone, organs, water, and connective tissue. It is a useful number for nutrition planning since protein requirements and many supplement recommendations are given per kilogram of lean mass, not total weight. For a 90kg person carrying 25% body fat, LBM is 67.5kg, and their protein target would be based on that rather than 90kg.
Different formulas produce slightly different results. Boer (1984) is considered more accurate for muscular individuals; James (1976) for leaner people; Hume (1966) for general use. The differences are typically small (1-3 kg). If you do not know your body fat percentage, these height-weight formulas give a reasonable estimate - just not as precise as a body composition scan.
Frequently Asked Questions
How is LBM different from fat-free mass?
They are often used interchangeably, but technically lean body mass includes essential fat (around 3% for men, 12% for women) stored in the nervous system and organs. Fat-free mass excludes all fat. For practical fitness use, the terms mean the same thing.
Why do I need LBM for protein intake?
Protein recommendations for muscle gain (1.6-2.2g per kg) are meant to be applied to lean mass, not total body weight. Applying them to total weight for someone carrying significant body fat would overshoot the actual muscle-supporting requirement.
Can I improve my LBM without losing weight?
Yes - body recomposition. Building muscle while losing fat can keep scale weight stable while improving composition and increasing LBM. It happens most reliably in people new to resistance training, after a significant break, or on a small calorie surplus.