What is lean body mass?

Lean body mass (LBM) is the total weight of everything in your body except fat — your muscles, bones, organs, water, and connective tissue. It is the opposite of fat mass, and together they make up your total body weight. Knowing your lean mass is useful for setting protein targets, planning training, and tracking whether weight changes come from muscle or fat.

How it is calculated

This calculator uses the Boer formula, a widely used equation that estimates lean mass from your sex, weight, and height. For men, LBM = (0.407 × weight in kg) + (0.267 × height in cm) − 19.2; for women, LBM = (0.252 × weight in kg) + (0.473 × height in cm) − 48.3. The remainder of your body weight is your estimated fat mass.

Why lean body mass matters

Lean mass drives your resting metabolism — more muscle means you burn more calories even at rest. During weight loss, the goal is to lose fat while preserving lean mass, which is why adequate protein and strength training are so important. Tracking LBM alongside body fat percentage gives a clear view of changes in body composition.

Frequently asked questions

How accurate is the estimate?

Formula-based estimates are good for tracking trends but are less precise than body-composition scans such as DEXA. They work best for people of average build.

How do I increase lean body mass?

Progressive strength training combined with enough protein and a small calorie surplus is the most reliable way to build lean muscle over time.

Disclaimer: This calculator provides estimates for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making health decisions.