Overview
Lean body mass (LBM) is everything in your body that isn't fat — muscle, bone, organs and water. Knowing it helps set protein needs, dose certain medications and track whether you're losing fat or muscle.
How it's calculated
Enter your sex, weight, height and body-fat percentage. We compute LBM two ways — the Boer formula (from height and weight) and directly from your body-fat figure — and show your fat mass for comparison.
Boer (male): 0.407×kg + 0.267×cm − 19.2 Boer (female): 0.252×kg + 0.473×cm − 48.3 LBM = weight × (1 − bodyfat%)
How to read your result
If you know your body fat, the direct LBM figure is usually the most accurate; the Boer estimate is a useful cross-check when you don't. When dieting, the goal is to lose fat mass while keeping LBM steady.
Frequently asked questions
LBM vs fat-free mass — same thing?
Almost. Fat-free mass excludes all fat; LBM technically includes a small amount of essential fat. In practice the terms are used interchangeably.
Which estimate should I trust?
If you have a reliable body-fat measurement, the LBM-from-body-fat figure is best. Otherwise the Boer formula gives a solid height-and-weight estimate.
Why does LBM matter?
It drives protein needs, reflects training progress, and on a diet it tells you whether you're losing fat or muscle — the difference between a good and bad cut.
Sources & references
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes. Am J Physiol. 1984;247(4):F632-F636.
Medical disclaimer
This calculator is for general educational purposes only and is not medical advice. Estimates are based on population formulas and may not fit your individual situation. Consult a qualified healthcare or fitness professional before making health, nutrition or training decisions.