Lean Body Mass Calculator
Estimate your lean body mass — muscle, bone, organs, and water, everything but fat — using the Boer formula.
The Boer formula
Women: LBM = 0.252×kg + 0.473×cm − 48.3
If you know your body fat percentage, LBM = weight × (1 − body fat) is more accurate — get body fat from the body fat calculator.
Man, 178 cm, 80 kg: 0.407×80 + 0.267×178 − 19.2 = 32.6 + 47.5 − 19.2 = ~60.9 kg lean, about 19 kg fat (24%).
Woman, 5'6" (66 in), 145 lb. Converted to metric: height = 66 × 2.54 = 167.6 cm; weight = 145 × 0.453592 ≈ 65.8 kg.
0.252 × 65.8 + 0.473 × 167.6 − 48.3 = 16.6 + 79.3 − 48.3 = ~47.6 kg lean, which converts back to about 104.9 lb lean of her 145 lb total — a lean mass percentage of 47.6 ÷ 65.8 ≈ 72.3%, versus about 76% for the male example above. That gap is consistent with the formula's different constants for women, reflecting a higher typical essential fat percentage.
Why lean mass is the number to protect
When people say they want to "lose weight," they almost always mean lose fat while keeping muscle. Lean body mass is that muscle-plus-everything-else — and it's the engine of your metabolism and strength. In a diet, protecting LBM is the whole game: hit your protein target (often set per pound of LBM), keep lifting, and avoid crash deficits that strip muscle along with fat. Tracking LBM alongside body fat over time shows whether a program is working even when scale weight barely moves.
Lean mass percentage by body fat category
| Category | Men (LBM %) | Women (LBM %) |
|---|---|---|
| Essential fat | 95–98% | 87–90% |
| Athletes | 87–94% | 80–86% |
| Fitness | 83–86% | 76–79% |
| Average | 76–82% | 69–75% |
| Above-average body fat | Below 76% | Below 69% |
This is simply the complement of the body fat calculator's categories (100% minus body fat %) — the two pages are two views of the same number.
Common lean mass mistakes
- Treating the Boer estimate as exact. It's a population-average formula from height, weight, and sex; a body-fat-based calculation is more accurate for any individual whose build differs from that average.
- Equating lean body mass with muscle mass. LBM also includes bone, organs, and body water — muscle is only part of the total.
- Setting protein targets off total body weight at a high body-fat percentage. Basing the target on LBM instead avoids overestimating protein needs, since fat tissue requires little protein to maintain.
Frequently asked questions
What is lean body mass?
Everything that isn't fat — muscle, bone, organs, water. Total weight minus fat mass.
Why does it matter?
It drives metabolism and strength; preserving it while losing fat is the goal of good dieting.
How is it calculated?
Boer formula from height/weight/sex, or weight × (1 − body fat %) if you know your body fat.
Is lean body mass the same as muscle mass?
No — LBM also includes bone, organs, and body water; muscle mass is only one component of the total.
Why might the two calculation methods disagree?
The Boer formula is a population average; a body-fat-based calculation uses your actual estimated body fat, so it's generally more accurate for anyone who differs from that average build.
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Medical disclaimer: A formula-based estimate, not a clinical measurement or medical advice. Formula: Boer (1984). Last reviewed: September 2026.