Lean Body Mass Calculator

Lean body mass is your total body weight minus the mass of your body fat. It includes muscle, bone, organs, connective tissue and the water in your body. It is sometimes called fat free mass.

Clinicians and coaches use it to dose some medications, set protein and calorie targets, and track whether weight changes come from muscle or fat. Because muscle drives metabolism, LBM is a better fitness yardstick than scale weight alone.

By default it uses the Boer formula, which estimates LBM from your weight, height and sex. If you enter a measured body fat percentage, it skips the estimate and computes lean mass directly as weight times one minus your body fat fraction.

It is a population estimate, so it can be off for very muscular, very lean or very heavy people. Entering a body fat percentage from calipers, a Navy tape estimate or a DEXA scan gives a far more accurate result.

No. The calculation runs entirely in your browser. Your weight, height and body fat figures never leave your device.

No. This tool is for general information and fitness tracking only and is not medical advice. Talk to a doctor or registered dietitian before making decisions about medication dosing, training or diet.