Lean Body Mass Calculator

Our Lean Body Mass tool estimates your LBM by using your weight, height, sex, and age. It also shows results from several different calculation methods for easy comparison.

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Lean body mass represents the portion of your body weight that isn’t fat. It includes bones, muscles, blood, skin, organs and water, while excluding all body fat. Typically, LBM accounts for about 60‑90 % of total weight, with men usually having a higher share than women. Dosages of certain water‑soluble anesthetics and some clinical assessments are based on LBM. In everyday fitness, most people focus on body‑fat percentage rather than LBM. To determine your body‑fat level, try our body‑fat calculator or ideal‑weight calculator.

Multiple formulas have been developed for calculating estimated LBM (eLBM) and the calculator above provides the results for all of them.

Lean Body Mass Formulas for Adults

The Boer Formula:¹

For males:

eLBM = 0.407W + 0.267H - 19.2

For females:

eLBM = 0.252W + 0.473H - 48.3

The James Formula:²

For males:

eLBM = 1.1W - 128( W H ) 2

For females:

eLBM = 1.07W - 148( W H ) 2

The Hume Formula:³

For males:

eLBM = 0.32810W + 0.33929H - 29.5336

For females:

eLBM = 0.29569W + 0.41813H - 43.2933

Lean Body Mass Formula for Children

The Peters Formula:⁴

According to the author, the following equation can be used for kids up to 13‑14 years old. It calculates an estimated LBM (eLBM) from a predicted extracellular volume (eECV) using this formula:

eECV = 0.0215·W0.6469·H0.7236

eLBM = 3.8·eECV

In the formulas above, W is the body weight in kilogram and H is the body height in centimeter.

Lean Body Mass vs. Fat Free Mass

People frequently treat lean body mass and fat‑free mass as synonyms, but technically they differ slightly.

LBM comprises the weight of bones, muscles, water, ligaments, tendons and internal organs. The essential fat inside those organs is counted as part of LBM, whereas the subcutaneous fat covering the organs is excluded.

Fat‑free mass equals total body weight minus all fat, essential fat included. In other words, if you remove the essential fat from LBM you obtain fat‑free mass. The gap between LBM and fat‑free mass is roughly 2‑3 % for men and 5‑12 % for women.

1. Boer P. "Estimated lean body mass as an index for normalization of body fluid volumes in man." Am J Physiol 1984; 247: F632-5
2. James, W. "Research on obesity: a report of the DHSS/MRC group" HM Stationery Office 1976
4. Hume, R "Prediction of lean body mass from height and weight.". J Clin Pathol. 1966 Jul; 19(4):389-91.
5. A. M. Peters, H. L. R. Snelling, D. M. Glass, N. J. Bird "Estimation of lean body mass in children". British Journal of Anaesthesia1 06(5): 719-23 (2011).

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