Formula, in Body Composition
Lean Body Mass Formula (Boer)
Lean body mass is everything you're not made of fat: muscle, bone, organs, water. The Boer equation uses height and weight; it's the most accurate non-imaging predictor for adults.
3 variables. Published Mar 12, 2026. Updated May 10, 2026. By AI Fit Hub.
Male: LBM = 0.407·mass_kg + 0.267·height_cm − 19.2
Female: LBM = 0.252·mass_kg + 0.473·height_cm − 48.3 Variables
LBM
Lean Body Mass
Kilograms of fat-free mass: muscle, bone, organs, intracellular water. Roughly 78–88% of body mass in average adults; 92%+ in elite athletes.
mass_kg
Body mass
Total body weight in kilograms.
height_cm
Standing height
Centimeters, measured barefoot.
Step by step
- 1
Pick the equation that matches biological sex. Sex-specific coefficients exist because average body composition differs.
Male: 0.407 weight coefficient, 0.267 height coefficient.
- 2
Multiply body mass in kg by the weight coefficient.
Male, 80 kg: 80 × 0.407 = 32.56 kg.
- 3
Multiply height in cm by the height coefficient and add.
178 cm × 0.267 = 47.53. Running total: 80.09 kg.
- 4
Subtract the sex-specific constant.
Male: 80.09 − 19.2 = 60.89 kg LBM. Body fat ≈ 80 − 60.89 = 19.11 kg, or 23.9%.
Worked example
Male, 80 kg, 178 cm
Sex
Male
Weight (kg)
80
Height (cm)
178
LBM = 0.407·80 + 0.267·178 − 19.2 = 32.56 + 47.526 − 19.2 = 60.89 kg
Lean mass 60.89 kg; implied fat mass 19.11 kg (23.9%). Compare with caliper or DXA to validate.
Common variations
Run the numbers next
- Body Composition Body Fat Percentage Calculator
Estimate body fat percentage using the U.S. Navy circumference method.
- Body Composition FFMI Calculator
Calculate Fat-Free Mass Index to gauge muscularity and compare against natural benchmarks.
Sources
- Boer P. Estimated lean body mass as an index for normalization of body fluid volumes in humans , American Journal of Physiology (1984)
- Quantification of lean bodyweight , Clinical Pharmacokinetics (2005) — Janmahasatian et al.