Health & Fitness
Lean Body Mass Calculator - Boer, James & Hume Formulas
Calculate lean body mass (LBM) using the Boer, James, and Hume formulas from weight and height. Includes fat-free mass estimate for male and female.
Weight (kg) must be a positive number.
These are population-based estimates. Body composition formulas vary in accuracy by individual. For precise measurements, use DEXA or hydrostatic weighing.
LBM measurement methods
| Method | Accuracy | Notes |
|---|---|---|
| DEXA (Dual-energy X-ray absorptiometry) | Very high (±1–2%) | Gold standard; requires clinical equipment |
| Hydrostatic (underwater) weighing | High (±2–3%) | Measures body density; requires pool and submersion |
| BIA (Bioelectrical impedance analysis) | Moderate (±3–5%) | Consumer scales; affected by hydration, meal timing |
| Skinfold calipers | Moderate (±3–4% with skilled tech) | Cheap and portable; technician skill-dependent |
| Formula (this tool) | Rough estimate (±5–10%) | Uses height and weight only; no body composition data |
Creatine and water retention
Creatine supplementation causes the body to retain water in muscle cells, which increases total body weight and LBM as measured by scale-based methods (like BIA). This weight gain (typically 1–3 kg in the first week of loading) is not muscle tissue - it is intracellular water. DEXA scans distinguish lean soft tissue from bone, which helps contextualize such changes more accurately.
Clinical applications
LBM is used in healthcare for precise dosing and planning:
- Pharmacology: many IV medications (aminoglycosides, vancomycin, chemotherapy agents) are dosed per kg of LBM or "adjusted body weight" to avoid overdosing obese patients
- Mechanical ventilation: tidal volume settings in ICU ventilators are calculated per kg of ideal body weight (closely related to LBM)
- Nutrition / TPN: total parenteral nutrition protein requirements are calculated per kg of LBM or adjusted weight
- Fitness tracking: monitoring LBM over time (via DEXA or calipers) distinguishes muscle gain from fat gain during a bulk
What is lean body mass?
Lean body mass (LBM), also called fat-free mass, is your total body weight minus body fat. It includes muscle, bone, organs, and water. LBM is used in pharmacology for drug dosing, and in fitness to track muscle gain.
Formulas
Boer formula (1984)
- Male: LBM = 0.407·W + 0.267·H − 19.2
- Female: LBM = 0.252·W + 0.473·H − 48.3
James formula (1976)
- Male: LBM = 1.1·W − 128·(W/H)²
- Female: LBM = 1.07·W − 148·(W/H)²
Hume formula (1966)
- Male: LBM = 0.3281·W + 0.3393·H − 29.5336
- Female: LBM = 0.2297·W + 0.3122·H − 14.0299
W = body weight in kg, H = height in cm
Which formula should I use?
The Boer formula is generally considered the most accurate for adults of average build. The calculator shows all three and their average for comparison.