Calculate your lean body mass — everything that isn't fat. Use this for precise protein targeting and tracking body recomposition.
Lean body mass = total weight minus fat. If you weigh 80 kg at 20% body fat, your LBM is 64 kg. Use LBM — not total weight — for precise protein targets (2.0-2.4g per kg LBM during a cut) and metabolic rate calculations.
Written by Ash K · Last updated: June 2026 · Sources cited below
Lean body mass (LBM) is everything in your body that isn't fat: muscle, bone, water, organs, connective tissue. It's the number that tells you what your scale weight actually consists of — and why two people at the same weight can look completely different.
This calculator estimates your lean body mass using the Boer formula, which research has shown to be the most accurate predictive equation for LBM estimation across diverse populations.
Key Takeaway: Lean body mass = total weight minus fat weight. If you weigh 80 kg at 20% body fat, your LBM is 64 kg (the muscle, bone, water, and organs) and your fat mass is 16 kg. LBM is more useful than total weight for setting protein targets, assessing fitness progress, and understanding body composition.
Enter your weight, height, sex, and (optionally) body fat percentage. The calculator estimates your LBM two ways:
Without body fat %: Uses the Boer formula — a predictive equation based on height and weight validated against DEXA scans.
With body fat %: Direct calculation — LBM = weight × (1 − body fat %). More accurate if you have a reliable body fat measurement from a DEXA scan, skinfold calipers, or our body fat calculator.
What Makes Up Lean Body Mass
For men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
For women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3
The Boer formula was published in 1984 and validated against body composition measurements. It outperforms older equations (James, Hume) in accuracy for most populations, though all predictive formulas have a margin of error of ±2–5%.
| Category | Men — LBM % of total weight | Women — LBM % of total weight |
|---|---|---|
| Athletic | 80–90% | 75–85% |
| Fit | 75–85% | 70–80% |
| Average | 70–80% | 65–75% |
| Above average body fat | 60–70% | 55–65% |
Note: Women naturally have lower LBM percentages than men due to essential fat differences. Women require approximately 10–13% essential body fat for hormonal health compared to 2–5% for men. This is biological, not a fitness shortcoming.
Why Lean Body Mass Matters: Three Key Uses
Protein targeting. Evidence-based protein recommendations for muscle building and retention are calculated per kilogram of lean body mass, not total weight. The recommendation of 2.0–2.4 g/kg LBM during a calorie deficit (Helms et al., 2014) gives a more precise target than weight-based calculations that include fat mass.
Example: 90 kg person at 25% body fat → LBM = 67.5 kg → protein target = 135–162g. Using total weight would give 180–216g — unnecessarily high.
Metabolic rate accuracy. LBM is the primary driver of basal metabolic rate. Two people at 80 kg with different LBM have different BMRs. The Katch-McArdle BMR formula uses LBM directly: BMR = 370 + (21.6 × LBM in kg). For a more detailed metabolic calculation, see our TDEE calculator.
Fitness progress tracking. If you're training and your scale weight stays the same for 8 weeks, are you making progress? If your LBM increased by 2 kg and fat decreased by 2 kg, that's excellent body recomposition — invisible to the scale, visible in lean mass tracking.
Tip: Track LBM over time rather than total weight. Recomposition — gaining muscle while losing fat — is the goal for most people. LBM is the only metric that captures it. Use our macro calculator to set protein targets based on your LBM result.
If you know your body fat percentage, the direct calculation is simpler and more accurate:
LBM = total weight × (1 − body fat fraction)
Example: 75 kg at 22% body fat → 75 × 0.78 = 58.5 kg LBM
The accuracy of this method depends entirely on the accuracy of your body fat measurement. DEXA scans are the gold standard (±1–2% error). Navy method and skinfold calipers are reasonable estimates (±3–5% error). Bioelectrical impedance scales are unreliable (±5–8% error depending on hydration).
Bottom Line: Your lean body mass is what matters for protein targeting, metabolic rate, and fitness progress — not your scale weight. Calculate it here, then use the result to set precise macro targets and track real body composition changes over time.
How do I calculate my lean body mass?
Two methods: (1) If you know your body fat percentage, multiply your total weight by (1 − body fat %). (2) If you don't, use the Boer formula in this calculator, which estimates LBM from your height, weight, and sex.
What is a good lean body mass?
It depends on your sex and fitness level. For men, LBM of 75–85% of total weight is fit; for women, 70–80%. These ranges shift based on age, training history, and genetics.
How do I calculate lean body mass with body fat percentage?
LBM = total weight × (1 − body fat as decimal). Example: 180 lbs at 20% body fat → 180 × 0.80 = 144 lbs lean body mass.
Should I use lean body mass for protein calculations?
Yes — it's more precise. Research recommends 1.6–2.2 g protein per kg of LBM for muscle building, and 2.0–2.4 g/kg LBM during calorie restriction to preserve muscle.
This calculator provides estimates. For precise body composition measurement, consult a healthcare provider or exercise physiologist for DEXA scanning.
This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your health.