Lean Body Mass Calculator
LBM estimate using the Boer formula — weight minus fat mass.
Result
- Implied fat mass17.0 kg
- Implied body fat %22.6%
- LBM — Hume formula54.4 kg
- LBM — James formula59.0 kg
- Average across formulas57.2 kg
How to use this calculator
- Pick your sex and units.
- Enter weight and height.
- Use the same formula consistently when tracking changes over time.
About this tool
Lean body mass (LBM) is everything that isn't fat — muscle, bone, organs, water. Knowing your LBM is more useful than scale weight for tracking real progress, especially during cuts (you want to lose fat without losing LBM) or bulks (you want LBM to grow). Three formulas commonly used: Boer (most popular), Hume, and James. They give slightly different estimates because they were calibrated on different populations. For accurate LBM tracking, DEXA scans are the gold standard; these formulas are good ballparks for athletes and routine check-ins.
How it works — the formula
Boer (men): LBM = 0.407·weight(kg) + 0.267·height(cm) − 19.2
Boer (women): LBM = 0.252·weight(kg) + 0.473·height(cm) − 48.3Boer 1984 derived the formula from underwater-weighing data on healthy adults; it is now the dominant LBM equation in clinical pharmacy and fitness writing. Hume 1966 and James 1976 produce slightly different estimates because each was calibrated against a different reference population (Hume used hospitalized patients, James used a wider international cohort). For most healthy adults the three agree within 2–3 kg.
Worked examples
- Inputs:
- sex = male, weight = 80 kg, height = 178 cm
- Output:
- LBM (Boer) ≈ 60.9 kg; implied fat mass ≈ 19.1 kg (~23.9%)
- Inputs:
- sex = female, weight = 60 kg, height = 168 cm
- Output:
- LBM (Boer) ≈ 46.3 kg; implied fat mass ≈ 13.7 kg (~22.9%)
- Inputs:
- male, 75 kg → 73 kg at constant 175 cm
- Output:
- Boer LBM 58.1 kg → 57.2 kg; ~0.8 kg lean lost alongside ~1.2 kg fat lost
Limitations
- Formula accuracy degrades at extremes — below 10% body fat or above 40% body fat — where DEXA is the practical reference.
- None of the formulas account for ethnicity-specific frame differences or training history.
- Tracking LBM month-over-month is more meaningful than the absolute value; pick one formula and stay with it.
- Bioimpedance smart scales can vary ±5–8% with hydration alone — formulas are often more stable for trend tracking.
For clinical body-composition decisions, prefer DEXA, BodPod, or hydrostatic weighing. This calculator does not provide medical advice.
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