Fat-Free Mass Calculator

About this calculator

Fat-free mass (FFM) is a person’s total body weight minus the weight of their body fat, encompassing everything else — muscle, bone, organs, water, and connective tissue. It’s calculated either directly, by multiplying total body weight by (1 − body fat percentage), or estimated from body fat percentage measured by other methods like calipers, bioelectrical impedance, or DEXA scanning.

FFM is used in clinical and sports settings because it’s a better predictor of metabolic rate than total body weight alone — the Katch-McArdle formula for calculating basal metabolic rate, for instance, uses fat-free mass specifically because muscle and organ tissue burn far more calories at rest than fat tissue does. Athletes and strength trainees also track fat-free mass over time as a more meaningful measure of physique changes than scale weight alone, since it isolates changes in lean tissue from changes in body fat.