Enter your sex, height, and weight to calculate lean body mass and fat mass using the Boer formula.
How to Use the Lean Body Mass Calculator
Sex and units come first here too, since the formula itself differs by sex — height and weight fill in the rest.
Lean body mass is everything on the scale that isn't fat — muscle, bone, organs, water, all of it lumped together as "fat-free mass." It's a more stable number to track over time than total weight, since it doesn't move much day to day the way water weight and food in the gut do.
Men: LBM = 0.407W + 0.267H − 19.2
Women: LBM = 0.252W + 0.473H − 48.3W is weight in kilograms, H height in centimeters. This is the Boer formula, published by Dr. P. Boer in the American Journal of Physiology in 1984 and still widely used for its accuracy against DEXA-scan (dual-energy X-ray) reference measurements — the closest thing to a gold standard for body composition outside a research lab. Subtract the result from total weight and what's left is an estimate of fat mass.
A population-average formula, not an individual measurement. A precise reading of an individual's actual composition needs DEXA, hydrostatic weighing, or a comparable direct method — not an equation run on two numbers. Talk to a doctor or dietitian about what this estimate means for you specifically.