Fat Mass and Lean Mass Calculator

About this calculator

Total body weight is made up of two very different components: fat mass, the weight contributed by body fat, and lean mass (also called fat-free mass), which covers everything else — muscle, bone, organs, and water. Once you know your body-fat percentage, splitting the two is straightforward: fat mass = total weight × body-fat percentage, and lean mass = total weight − fat mass.

This breakdown matters more than total weight alone for tracking real physical progress, since two people at the same weight can have very different body compositions. This calculator takes your total weight and body-fat percentage and splits it into fat mass and lean mass instantly, which is useful for athletes and gym-goers tracking body recomposition, and for anyone following up on a DEXA scan, bioelectrical impedance (BIA) reading, or caliper measurement with a quick calculation.