Lean Body Mass Calculator

About Lean Body Mass

Lean body mass (LBM) represents everything in your body that isn't fat — muscle, bone, organ tissue, blood, and water. It is a critical metric for assessing metabolic health, because it is your lean tissue that drives resting energy expenditure. Knowing your LBM helps set accurate protein targets; a common recommendation is 1.6–2.2 g of protein per kilogram of lean mass for people seeking to build or preserve muscle. This is why our Protein Calculator and Macro Calculator both allow LBM-based calculations.

Three well-validated equations are used here. The Boer formula (1984) is widely cited in pharmacokinetic research for drug dosing based on body size. The James formula (1976) was one of the earliest practical models and is still used in anesthesia and critical care for calculating dosing of medications that distribute into lean tissue. The Hume formula (1966) is commonly used in kidney disease research because it correlates well with total body water. Because each was derived from different populations, they can give slightly different results — hence the value of comparing all three and using the average.

Lean body mass can also be estimated indirectly from body fat percentage. If you know your body fat percentage from a DEXA scan or from the US Navy method in our Body Fat Calculator, LBM = Total Weight × (1 − Body Fat%). These formula-based estimates work well for most people but may be less accurate for very lean athletes or people with unusual body proportions. For the most accurate measurement, DEXA scanning or hydrostatic weighing are recommended.

Formula Reference