What is Lean Body Mass (LBM)?

Lean Body Mass (LBM), often used interchangeably with "fat-free mass," represents the total weight of your body minus all the weight from fat mass. LBM includes the weight of your bones, organs, skin, muscle, and body water. It is one of the most important metrics for tracking the results of a fitness or nutrition program, as it provides a clearer picture of your body composition than a standard scale.

Why is LBM Important?

• Metabolic Rate: Muscle is metabolically active tissue. The more lean body mass you have, the higher your Basal Metabolic Rate (BMR) will be, meaning you burn more calories at rest. You can find out your specific resting metabolism with our BMR Calculator.
• Fitness Progress: When you're losing weight, you want to lose fat, not muscle. Tracking your LBM helps ensure your diet and exercise plan is preserving or building muscle.
• Health Assessment: While BMI is a useful screening tool, LBM provides a much better assessment of health, especially for athletic individuals who might be classified as "overweight" by BMI due to high muscle mass.

How is Lean Body Mass Calculated?

This calculator uses several different formulas to estimate LBM. While a DEXA scan is the gold standard for accuracy, these formulas can provide a useful and accessible estimation.

• U.S. Navy Method: This is a circumference-based method that first calculates your body fat percentage, then subtracts that from your total weight. It is generally considered more accurate than simple height-weight formulas. For a more detailed look at this method, see our dedicated Body Fat Calculator.
• Boer & Hume Formulas: These are scientifically validated formulas that estimate LBM using only your height and weight, making them quick and easy to use.