Lean Body Mass Calculator

No formula is perfect because LBM depends on individual body composition, hydration, and bone density. The three most-cited formulas (Boer, James, Hume) usually agree within 1-2 kg. Averaging them reduces formula-specific bias. If you've had a DEXA scan or BIA test, that exact number is more accurate.

Peters (2011) was developed primarily for paediatric drug-dosing calculations. It uses height and weight in a power equation. For adults it tracks closely with Boer; for children and adolescents it's the recommended choice. Enable it in Customize mode.

Common targets per kg of LEAN mass (not total weight): sedentary ~1.2, active 1.6, hard-training athletes 2.0-2.2. The calculator does this for you. Using LBM instead of total weight matters at higher body fat % — a 100 kg person at 35% body fat doesn't need protein for the 35 kg of fat they're carrying.

Yes — it's more useful than tracking weight alone. On a cut, you want LBM steady while total weight drops (fat loss without muscle loss). On a bulk, you want LBM going up faster than fat mass. These calculator estimates work for trend tracking but a DEXA scan every 3-6 months is the gold standard.

Technically: LBM includes about 3% 'essential' fat (cell membranes, brain, organs). Fat-free mass excludes all fat. In practice the difference is small (1-2 kg) and the terms are used interchangeably in fitness contexts.

Boer is the most cited in recent medical literature, especially for drug dosing calculations. James was developed using athletes so it can underestimate LBM in sedentary people. Hume is the oldest but holds up well across populations. For general fitness use, the average of all three is the safest estimate.