Lean Body Mass Calculator

The Lean Body Mass Calculator computes a person's estimated lean body mass (LBM) based on body weight, height, gender, and age. For comparison purposes, the calculator provides the results of multiple formulas.

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Lean body mass (LBM) is a part of body composition that is defined as the difference between total body weight and body fat weight. This means that it counts the mass of all organs except body fat, including bones, muscles, blood, skin, and everything else. While the percentage of LBM is usually not computed, it on average ranges between 60-90% of total body weight. Generally, men have a higher proportion of LBM than women do. The dosages of some anesthetic agents, particularly water-soluble drugs, are routinely based on the LBM. Some medical exams also use the LBM values. For body fitness and routine daily life, people normally care more about body fat percentage than LBM. To compute body fat, consider using 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

The author suggests that this formula is applicable for children aged 13-14 years old or younger. The formula is used to compute an eLBM based on an estimated extracellular volume (eECV) as follows:

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

Lean body mass and fat free mass are often used interchangeably. While this is unlikely to cause issues in most cases, the two are not exactly the same.

Lean body mass includes the combined mass of bones, muscles, water, ligaments, tendons, and internal organs. Internal organs include some essential fat and the mass of this fat is included within the measurement of lean body mass. Although internal organs also have surrounding subcutaneous fat, this fat is not included within the measurement of lean body mass.

Fat free mass is calculated as the difference between total body mass and all fat mass including essential fat. This is the difference between fat free mass and lean body mass. Subtracting the mass of essential fat from lean body mass yields fat free mass. The difference between lean body mass and fat free mass amounts to approximately a 2-3% difference in men and 5-12% difference in 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
3. Hume, R "Prediction of lean body mass from height and weight.". J Clin Pathol. 1966 Jul; 19(4):389-91.
4. 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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