Lean body mass (LBM) is your total body mass minus the mass of any fat. So, it includes the weight of your muscles, tendons, ligaments, bones, blood, skin, and anything else that isn't fat.

Since it constitutes the functional part of your body, i.e. everything that performs work, burns energy, and sustains life, it's an important metric. Particularly in medical settings, where correct dosage is often calculated with respect to a patient's lean body mass rather than their overall body weight. Athletes and sportspeople are also often concerned with lean body mass, since excess non-functional weight is often detrimental to performance.

The LBM equation (where BW = body weight and BF = body fat) is simple:

LBM = BW − BF

However, measuring lean body mass in practise is challenging. The most accurate measurement method is a DEXA (Dual-energy X-ray absorptiometry) scan. However, this is very expensive and rarely accessible, so many formulae, usually based on a combination of height, weight, sex, and age, have been developed.

Our calculator estimates lean body mass using five different models.

Hume

The Hume model, generally considered one of the more conservative, is based on research of 29 men ranging in age from 40 to 77, and 27 females ranging in age from 37 to 80.

Hume measured the height and weight and total body water of each of the study's participants. Since lean body mass is consistent in its water content it was possible to then accurately calculate lean body mass based on findings from earlier researchers. Specifically, lean body mass is approximately 73.2% water

From here, Hume used multiple linear regression to derive lean body mass equations.

For women:

LBM = 0.29569 W + 0.41813 H − 43.2933

For men:

LBM = 0.32810 W + 0.33929 H − 29.5336

where:

LBM = Lean Body mass

W = weight in kilograms

H = height in centimeters

Strengths

Because the study participants were aged between 37 and 80, Hume is a popular choice for middle-aged and older people.

Being a conservative model, it's also popular with those who don't want to overestimate muscle mass.

Weaknesses

Although Hume's study closely reflects the correlation between height and weight and lean body mass for its original participants, people in the modern day are generally taller and the average body composition is different than it was in 1966.

It is also worth noting that the youngest study participant was 37 years old and the mean age of the group was 60. Humans tend to hit peak bone mineral density and muscle mass potential in their late 20s to early 30s, so his formula may underestimate lean mass in younger people. For similar reasons, muscle mass in older individuals (70+) may be overestimated.

Boer

Boer's formula was derived in the context of calculating water-soluble drugs and anesthesia. His study determined that lean body mass is a good proxy for total body water.

Boer measured height, weight, and body water volume of 47 men and 40 women, ranging in age from 19 to 72, and used multiple linear regression to derive his formulae.

For women:

LBM = 0.252 W + 0.473 H − 48.3

For men:

LBM = 0.407 W + 0.267 H − 19.2

Strengths

Since participants as young as 19 were included in Boer's study, it is much more suitable for a wider population than Hume's, which focused entirely on middle-aged and older adults.

Boer's model was specifically devloped in order to calculate drug dosing and clearance, and as such it's been rigorously tested in the field.

Weaknesses

Since Boer's study was carried out in the Netherlands, it is biased towards Northern European body types.

Boer's formulae will begin to struggle at low or high BMIs (less than 16 or greater than 40), since the relationship between height, weight, and water volume becomes non-linear at these points.

James

James' formula appears in a 1976 UK government report: "Research on obesity: A report of the DHSS/MRC group".

It was designed to take into account the non-linear relationship between weight and muscle in obese people. Specifically, that as a person becomes more obese, the percentage of their weight that is lean mass decreases.

For women:

LBM = 1.07 W − 148 ×

(

W H

) 2

For men:

LBM = 1.10 W − 128 ×

(

W H

) 2

Strengths

Unlike the Hume and Boer models, the James model is non-linear. Specifically, it doesn't assume that a person's ratio of lean tissue to fat remains constant as total body weight increases.

For those with BMIs between 25 and 35 it tends to be more accurate than the above models.

Weaknesses

Because of the way the formula is derived it begins to struggle at higher BMIs and nonsensically assumes that a heavier person will have less overall lean body mass than a lighter person. Specifically, the formula becomes inaccurate for those with BMIs higher than about 43 for men and about 37 for women.

Janmahasatian

Janmahasatian's team derived a non-linear formula useful for estimating lean body mass in those with very low and very high BMIs.

The team took height and weight measurements of 373 patients, ranging in age from 18 to 82 years, whose BMIs were between 17.1 and 69.9. They used sophisticated modern methods to measure their lean body mass.

Their research generated the following formulae for lean body mass estimates.

For women:

LBM =

9.27 × 103 × W 8.78 × 103 + 244 × BMI

For men:

LBM =

9.27 × 103 × W 6.68 × 103 + 216 × BMI

Strengths

Since BMI is included in the formula, this model accounts for the fact that, as body weight increases, the ratio of lean mass to fat changes.

Unlike the James model, the Janmahasatian can cope with higher BMIs.

Weaknesses

Although the model was developed by studying individuals with a wide range of body weights and BMIs, the ranges used to evaluate the model were more limited.

Peters

The formula developed by Peters and team is intended for use by younger individuals (between 1 month and up to 15 years).

To calculate lean body mass in children we first calculate Estimated Extracellular Volume (eECV):

eECV = 0.0252 × W0.6469 × H0.7236

Then we can calculate lean body mass from the body surface area:

LBM = 3.8 × eECV

Strengths

A single formula can be used for both girls and boys.

Weaknesses

The accuracy of the model is less robust in children with very high BMIs.

The formula may be less accurate for precocious older children.

Notes

A weakness common to all the models is the assumption that everybody has the same amount of muscle for their size. This means, for example, that a bodybuilder and sedentary person of the same height and weight would get the same lean body mass result.

Form Fields

Weight

Enter your weight in pounds, kilograms, or stones and pounds.

Height

Enter your height in either feet and inches or centimeters.

Sex

Specify male or female.

Age

Enter your age as a whole number. Accepted ages are 0 to 85.

Example Results

The number of models shown in the results will vary according to input values. For example, the James formula is unsuitable for low and high BMIs, and those aged 14 or below will only see results from Peters model, which is the only model specifically designed for children.

Adult Example

Assuming a 35-year-old woman who is 5 feet 3 inches (160 centimeters) tall and weighs 140 pounds (63.5 kilograms):

Child Example

Assuming a 13-year-old child who is 5 feet 2 inches (1557.5 centimeters) tall and weighs 118 pounds (3.5 kilograms):

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Further reading

Prediction of lean body mass from height and weight (Hume)

Estimated lean body mass as an index for normalization of body fluid volumes in humans (Boer)

Quantification of Lean Bodyweight (Janmahastian)

Estimation of lean body mass in children (Peters)