The Boer formula is a multiple regression equation developed from body composition research. It estimates lean mass using sex, height, and weight as predictors. The formula was derived from a sample of healthy adults and is most accurate near the population average. For the same inputs, men and women produce different estimates because typical body composition ratios differ by sex. If you provide body fat percentage from a DEXA scan or caliper measurement, the calculator uses simple subtraction to back out absolute fat mass in pounds.
The Boer formula works well near the population average but can miss by several pounds for very muscular, obese, or very lean individuals. If you already have a DEXA or bioimpedance result, use that instead. Otherwise, compare this estimate against other formulas (Katch, Hume) as a sanity check.
Both matter. LBM guides protein targets (roughly 0.7–1 gram per pound of LBM), while body fat percentage tells you whether you're gaining muscle or fat during a bulk or cut. Ideally, monitor both alongside progress photos and strength gains.
Most people don't know their body fat percentage without a DEXA, caliper, or bioimpedance test. The calculator estimates LBM from height and weight alone so you get a useful result immediately. If you've had a body composition assessment, drop in the percentage for a more direct calculation of fat mass.
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.