Lean Body Mass Calculator
Lean body mass (LBM) is your total body weight minus all fat mass, including muscles, bones, organs, and water. This calculator estimates your LBM using three established medical formulas to give you a comprehensive picture of your body composition.
Lean body mass is an important metric for understanding your body composition beyond what the scale shows. It includes everything in your body except stored fat: skeletal muscle, organs, bones, blood, water, and connective tissue. Knowing your LBM helps with setting appropriate protein intake, calorie targets, and medication dosing.
The three formulas used here each approach LBM estimation differently. The Boer formula (1984) uses a linear relationship between weight, height, and LBM. The James formula uses a quadratic approach based on the ratio of weight to height. The Hume formula (1966) is a regression-based estimate. All three are reasonably accurate for individuals of normal to moderately overweight body composition.
For very lean or very obese individuals, these formulas may be less accurate. Direct measurement methods such as DEXA scans, underwater weighing, or bioelectrical impedance analysis provide more precise body composition data. These calculator estimates are best used as a general guideline for nutritional and fitness planning.