Lean Body Mass (LBM) represents the weight of everything in your body that isn't fat. This includes your muscles, bones, organs, skin, and water. Understanding your LBM is often more valuable than tracking your total body weight because it helps you see the quality of your weight. For example, if you're trying to lose weight, you want to lose fat while preserving LBM. If you're trying to gain weight, you want to increase your LBM. This calculator uses the Hume formula to provide a reliable estimate of your LBM.