What is Lean Body Mass (LBM)?
Lean Body Mass (LBM) is the amount of weight you carry on your body that isn't fat. This includes your muscles, bones, organs, and body water. While Body Mass Index (BMI) tells you if you are "overweight," Lean Body Mass tells you how much of your weight is actually functional, metabolically active tissue.
Why Calculate LBM?
For athletes and bodybuilders, LBM is a more critical metric than total body weight. If you are on a weight loss program, the goal is typically to lose body fat while preserving as much Lean Body Mass as possible. A drop in LBM usually indicates that you are losing muscle mass, which can slow down your metabolism.
The Formulas Used
Because every person's body composition is unique, scientists have developed several clinical formulas to estimate LBM based on height, weight, and biological sex. Our calculator provides an average of the three most trusted equations:
1. The Boer Formula
Developed in 1984, the Boer formula is widely used in medical environments to estimate lean mass and calculate dosages for medications that do not distribute into fat tissue.
2. The James Formula
The James formula is often used to estimate lean mass in individuals with a normal range of body fat. It tends to be less accurate at the extremes of obesity.
3. The Hume Formula
The Hume formula, developed in 1966, is a classic anthropometric equation used primarily in physiological research studies.
LBM and Basal Metabolic Rate (BMR)
Your Lean Body Mass is the primary driver of your metabolism. Muscle tissue burns significantly more calories at rest than fat tissue. By increasing your LBM through resistance training and adequate protein intake, you can effectively "increase your engine size," allowing you to burn more calories every day even when you aren't exercising.