# Lean Body Mass Calculator (Boer / Hume / James) Estimate your lean body mass (LBM) from sex, age, weight and height using three clinical formulas side by side, with derived body-fat percentage. > Canonical page: https://elysiatools.com/en/tools/lean-body-mass-calculator - **Category:** Health - **Keywords:** lean body mass, lbm calculator, fat free mass, boer formula, hume formula, james formula, body composition, muscle mass ## Overview The Lean Body Mass Calculator estimates your lean body mass (LBM) and derived body-fat percentage using three clinical formulas—Boer, Hume, and James—side by side. By inputting your sex, age, weight, and height in either metric or imperial units, you can instantly compare these established medical equations to better understand your body composition and track muscle mass. ## Inputs - **Sex** (select) - **Age** (number): e.g. 30 - **Body weight** (number): e.g. 70 - **Weight unit** (select) - **Height** (number): e.g. 175 - **Height unit** (select) - **Decimal places** (number) ## When to use - When tracking body composition changes during a fat loss or muscle building phase. - When calculating precise macronutrient targets or daily energy expenditure based on lean mass. - When comparing clinical formulas like Boer, Hume, and James to get a balanced estimate of fat-free mass. ## How it works - Select your sex and enter your current age. - Input your body weight and height, choosing either metric (kg, cm) or imperial (lb, in) units. - Adjust the decimal precision and run the calculation to view the side-by-side results of the Boer, Hume, and James formulas, along with your average lean body mass and estimated body fat percentage. ## Use cases - Fitness enthusiasts calculating lean mass to set accurate protein intake goals. - Nutritionists and dietitians estimating client body composition using clinical formulas. - Athletes tracking changes in muscle mass versus fat mass over a training cycle. ## Frequently asked questions ### What is Lean Body Mass (LBM)? Lean Body Mass is the weight of everything in your body except fat, including muscles, bones, organs, and water. ### What is the difference between the Boer, Hume, and James formulas? These formulas use slightly different mathematical coefficients based on historical clinical studies to estimate fat-free mass from height and weight. ### Which formula is the most accurate? The Boer formula is widely used as a clinical standard, but comparing all three side-by-side provides a more reliable average estimate. ### Does this calculator support imperial units? Yes, you can input weight in pounds (lb) and height in inches (in), which are automatically converted for the calculations. ### How is the body fat percentage derived? The calculator subtracts the estimated lean body mass from your total body weight to determine fat mass, then calculates it as a percentage of your total weight. ## Related tools - [Lotka–Volterra Interspecific Competition Simulator](https://elysiatools.com/en/tools/lotka-volterra-competition): RK4 simulation of two competing species with phase plane, isoclines, equilibrium, and automatic outcome classification. - [Extended BMR Calculator (Mifflin / Schofield Multi-Formula Comparison)](https://elysiatools.com/en/tools/basal-metabolic-rate-ext): Compare Mifflin-St Jeor, original and revised Harris-Benedict, Schofield (FAO/WHO/UNU), and Katch-McArdle BMR equations side by side with mean and spread in kcal/day. 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