Lean Body Mass Calculator
Show the math
What Your Result Means
- Lean Body Mass (LBM): Everything in your body except fat tissue — muscle, bone, organs, water, and glycogen. Higher LBM typically means more muscle and better metabolic health.
- LBM in kg: The same measurement converted to kilograms for international reference or use with metric-based formulas.
- LBM Percentage: Your lean mass as a percentage of total body weight. A higher percentage indicates greater muscularity; 70-85% is typical for fit adults.
- Fat Mass: When you provide body fat percentage, the calculator subtracts it to show absolute pounds of fat tissue.
How This Calculator Works
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.
Quick Questions
Why is my LBM estimate so high or low?
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.
Should I use LBM or fat percentage for fitness goals?
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.
Why don't you ask for body fat percentage by default?
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.
Sources
- Boer P. Estimating lean body mass. Br J Sports Med. 2004 (original research paper on the Boer regression formula)
- NIH: Body Composition (NIH National Center for Biotechnology Information on body composition measurement methods)
- CDC: Assessing Weight Status (CDC guidance on body composition and health assessment)
Method & review
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.