Lean Body Mass
Calculator

Lean body mass (LBM) is your total body weight minus your fat mass, so it includes muscle, bone, organs, and water content. Unlike total weight, LBM specifically reflects the metabolically active tissue that drives most of your calorie burn.

This calculator typically uses your body fat percentage (measured or estimated separately) and total weight, subtracting the fat portion to leave the lean portion, or applies a formula like Boer or James that estimates LBM from height, weight, and sex directly. Results can vary somewhat depending on which method feeds into the calculation.

Lean tissue burns significantly more calories at rest than fat tissue, so LBM is often used to set more personalized calorie and protein targets, especially for people with higher or lower than average body fat. Protein intake recommendations for muscle building, for instance, are frequently based on grams per kilogram of lean mass rather than total weight.

Yes, this is common: someone with lower body fat percentage will have higher lean body mass than someone at the same total weight with higher body fat. This is why total weight alone can be a poor indicator of fitness or metabolic health.

It can go either way: strength training combined with adequate protein while losing fat can preserve or even increase lean mass, while severe calorie restriction without exercise often leads to losing lean tissue along with fat. Monitoring both weight and estimated body fat gives a fuller picture than tracking weight alone.