Why anyone tracks lean mass
Lean body mass matters for two practical reasons. In the gym, it tells you whether weight loss is fat loss or muscle loss — the goal in most recomp programs is dropping fat while preserving LBM. In medicine, several drug dosages (chemotherapeutics, anaesthetics) are calculated against LBM rather than total weight, because the active fat-soluble compartment is much smaller than total body weight.
The Boer formula
Boer (1984) derived the most-cited published predictors against deuterium-dilution body composition data:
- Male: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
- Female: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3
From there, body fat percentage is straightforward: (total weight − LBM) / total weight, multiplied by 100.
Limits
The Boer formula was validated against a typical-composition adult cohort. It tends to underestimate LBM for trained athletes (who carry more muscle than the average for their height/weight) and overestimate LBM for sedentary adults at higher body weights. For an accurate reading, a DEXA scan, BodPod, or hydrostatic weighing through a sports medicine clinic gives a much better answer.