30-year-old male, 80 kg, 180 cm, no BF%
Input: Sex: male, Weight 80 kg, Height 180 cm
Output: Boer ≈ 61.7 kg; Hume ≈ 57.8 kg; James ≈ 64.0 kg; Janmahasatian ≈ 61.8 kg; average ≈ 61.3 kg
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Lean Body Mass Calculator
Estimate lean body mass (LBM) using Boer, Hume, James, and Janmahasatian formulas with side-by-side comparison.
About Lean Body Mass Calculator
The Lean Body Mass Calculator estimates the weight of your fat-free tissue — muscle, bone, organs, water — using four widely cited clinical equations. Boer (1984) and Hume (1966) are the most cited general-population formulas using weight, height, and sex. James (1976) is an older WHO-cited equation that tends to give slightly higher estimates. Janmahasatian (2005) is BMI-aware and preferred when BMI is elevated. If you know your body fat percentage (e.g. from the Body Fat Navy tool), the calculator also shows a more accurate direct LBM: weight × (1 − BF%/100). LBM is useful for setting protein targets and tracking muscle changes during recomposition. This calculator is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider before making decisions about your health.
Why use Lean Body Mass Calculator
- Four validated clinical formulas — Boer, Hume, James, Janmahasatian — calculated in one place.
- Direct method using body fat % when measured input is available, which is the most accurate.
- BMI-aware Janmahasatian equation handles obese subjects more reliably than purely linear formulas.
- Side-by-side comparison shows how much LBM estimates vary across methodologies.
- Useful for setting evidence-based protein targets (1.6-2.2 g/kg of lean mass).
- Privacy-first: anthropometric data never leaves your browser.
How to use Lean Body Mass Calculator
- Choose your unit system (kg/cm or lb/in).
- Select biological sex — all four formulas have sex-specific coefficients.
- Enter your current weight and height accurately.
- Optionally enter a measured body fat % to get a direct, more accurate LBM number.
- Compare the four formula results side by side to see the typical 1-3 kg variance between equations.
- Use the formula average for general planning, or the direct method when body fat % is known.
When to use Lean Body Mass Calculator
- Setting a daily protein target based on lean mass rather than total weight.
- Tracking muscle preservation during a fat-loss phase.
- Estimating drug dosing for medications that scale by lean mass (e.g., anesthesia).
- Comparing predictive LBM with a DEXA, BIA, or caliper measurement.
- Setting a realistic 'lean mass target' before starting a recomposition program.
- Assessing sarcopenia risk in older adults (LBM declines ~1% per year after 30).
Examples
28-year-old female, 65 kg, 165 cm, BF% 24
Input: Sex: female, Weight 65 kg, Height 165 cm, BF 24%
Output: Direct LBM = 65 × 0.76 = 49.4 kg (most accurate); formula average ≈ 47.9 kg
45-year-old male, 110 kg (obese), 178 cm
Input: Sex: male, Weight 110 kg, Height 178 cm
Output: Boer ≈ 73.3 kg; Janmahasatian ≈ 71.5 kg (preferred at high BMI); Hume ≈ 71.6 kg
Tips
- When BMI is over 30, weight the Janmahasatian estimate higher than Boer or Hume — it was specifically derived for obese subjects.
- Pair this tool with the Body Fat (Navy) calculator to get a measured BF% for the direct LBM method.
- Use LBM (not total weight) to anchor protein targets — typically 1.6 to 2.2 g per kg LBM.
- Track LBM trends over months, not weeks — formula noise is roughly ±1 kg.
- If your goal is muscle gain, expect realistic LBM gains of 0.25-0.5 kg/month for trained lifters.
Frequently Asked Questions
How accurate is this calculator?▾
Predictive formulas are typically within ±2-3 kg of DEXA-measured LBM for adults of normal-to-overweight BMI. The direct method using a measured body fat % is the most accurate.
Should I rely on this without a doctor?▾
For everyday fitness goals, yes — but for clinical contexts such as drug dosing, malnutrition assessment, or sarcopenia diagnosis, work with a qualified clinician using DEXA or BIA.
Are my measurements stored anywhere?▾
No. Calculations run entirely in your browser. No height, weight, or body fat data is transmitted to any server.
Which formula should I trust most?▾
For BMI under 30, Boer is the most commonly cited general-population formula. For BMI over 30, Janmahasatian was specifically derived for obese subjects and is more accurate. The direct method (weight × (1 − BF%/100)) is best when BF% is measured.
Can I use LBM to set my protein target?▾
Yes — current sports nutrition research supports 1.6-2.2 g protein per kg of lean body mass for muscle preservation and growth, particularly during fat loss.
Why do the four formulas disagree?▾
Each was derived from a different population sample (military, hospital, elderly, etc.) and uses different inputs. Disagreement of 1-3 kg is normal — the average is a reasonable consensus number.
Does LBM include water weight?▾
Yes. Lean body mass includes all non-fat tissue: muscle, bone, organs, blood, and intracellular and extracellular water — typically ~73% of LBM is water.
How often will my LBM change?▾
For trained lifters in caloric surplus, 0.25-0.5 kg/month of true LBM gain is realistic. For older adults, ~1% per year of LBM is naturally lost without resistance training.
Explore the category
Glossary
- Lean mass vs fat mass
- Lean mass is everything in the body that is not fat — muscle, bone, organs, and water. Fat mass is total adipose tissue. Total weight = lean + fat.
- Bioimpedance
- Bioelectrical impedance analysis (BIA) sends a tiny electrical current through the body and estimates lean mass from the electrical resistance; varies with hydration.
- DEXA scan
- Dual-energy X-ray absorptiometry — gold-standard imaging method for body composition; distinguishes bone, lean mass, and fat mass with sub-1% precision.
- Body composition
- Distribution of fat, lean mass, bone, and water — a more meaningful health metric than scale weight alone.
- BMI vs BFP
- BMI (weight ÷ height²) ignores composition; BFP (body fat percentage) is fat mass ÷ total mass and reflects composition directly.
- Sarcopenia
- Age-related loss of muscle mass and strength; LBM tracking helps detect it early in older adults.