HEALTH · LEAN BODY MASS
Lean Body Mass Calculator
Calculate your lean body mass — total weight minus body fat — using the Boer and James clinical formulas, in metric or imperial units.
About This Calculator
Lean body mass (LBM) is everything in your body except stored fat — muscle, bone, organs, blood, and water. Knowing your LBM helps inform protein targets, medication dosing by a clinician, and fitness tracking beyond the scale.
How It Works
Enter your height, weight, and biological sex. The calculator uses the Boer (1984) formula as primary and the James (1976) formula as secondary. Both are height-weight-sex equations validated against direct body composition measurements. Results are estimates — body composition methods like DEXA or hydrostatic weighing are more accurate.
The Formula
Boer (kg): men = 0.407·W + 0.267·H − 19.2 women = 0.252·W + 0.473·H − 48.3
- W
- body weight in kg
- H
- height in cm
Frequently Asked Questions
- What is lean body mass?
- Lean body mass is total body weight minus fat mass. It includes muscle, bone, connective tissue, organs, and fluids. A higher LBM-to-weight ratio generally indicates greater muscle mass relative to fat.
- Why does biological sex affect the result?
- The Boer and James formulas were derived from measurements of male and female populations and use different constants for each sex, reflecting typical differences in body composition.
- Why is the James formula sometimes unavailable?
- The James formula contains a squared weight-to-height ratio term that diverges at extreme weight or height combinations (very high BMI or very underweight). When this happens, only the Boer result is shown.