Skip to content
CalculatorBuddy

Lean Body Mass Calculator

Estimate lean body mass from height, weight, sex, and age. Compare Boer, James, Hume, and (for children) Peters formulas, with implied body fat, in US or metric units.

Maintained by CalculatorBuddy TeamEditorial methodology

Add as a preferred source on Google (opens in a new tab)

US Units

ExampleSample values — edit any field to see your result.

Sex used by adult formulas
Age 14 or younger?

Yes lists the Peters pediatric estimate first. Adult formulas remain visible only as clearly labeled comparisons.

ft
in
lbs

Results update as you type.

Lean body mass

127.4 lbs (80%)

Boer formula for adults; Peters formula when age 14 or younger. See the table for every formula.

Estimated result

Estimated body fat
20%

Saved calculations stay only in this browser. Share copies a link containing your entered values.

Compare scenarios

Keep a baseline, then change an assumption to see its effect side by side.

Lean body mass by formula

FormulaLean Body MassBody Fat
Boer127.4 lbs (80%)20%
James129.0 lbs (81%)19%
Hume120.4 lbs (75%)25%
Lean body mass127.4 lbs (80%)

This calculator estimates lean body mass (LBM) from height, weight, and sex, then shows implied body fat as the rest of your weight. Adults see Boer, James, and Hume side by side. If you are 14 or younger, Peters is listed first, with the adult formulas kept for comparison. Results are estimates for fitness and education — not a diagnosis.

Interpreting the table

The table makes the formula spread visible. An implied body-fat percentage is calculated as 100 minus the rounded lean-mass share. It is not an independent body-fat measurement. If a formula predicts zero, a negative value, or lean mass at or above total body weight, that percentage is labeled not meaningful.

Examples

Man, 5 ft 10 in, 160 lb (US default)

Height is 177.8 cm and weight is 160 / 2.2046 kg. Boer gives 127.4 lbs (80%) lean mass and 20% body fat. James is 129.0 lbs (81%) and Hume is 120.4 lbs (75%).

Man, 180 cm, 60 kg (metric default)

Boer is 53.3 kg (89%), James 51.8 kg (86%), and Hume 51.2 kg (85%). The same person marked age 14 or younger adds Peters at 49.5 kg (82%).

Girl, 4 ft 6 in, 70 lb, age 14 or younger

Peters (the pediatric row) is 59.4 lbs (85%). The adult formulas still appear for comparison: Boer 54.2 lbs, James 57.4 lbs, Hume 51.7 lbs.

Formula

All formulas use weight W in kilograms and height H in centimetres. US entries are converted with the rounded factor of 2.2046 pounds per kilogram.

Boer (adults)

Men:   eLBM = 0.407W + 0.267H − 19.2
Women: eLBM = 0.252W + 0.473H − 48.3

James (adults)

Men:   eLBM = 1.1W − 128(W / H)²
Women: eLBM = 1.07W − 148(W / H)²

Hume (adults)

Men:   eLBM = 0.32810W + 0.33929H − 29.5336
Women: eLBM = 0.29569W + 0.41813H − 43.2933

Peters (age 13–14 or younger)

eECV = 0.0215 × W^0.6469 × H^0.7236
eLBM = 3.8 × eECV

Lean-mass percent is the estimate divided by body weight, rounded to a whole percent. Body fat percent is 100 minus that figure.

These equations are population regressions, not measurements of an individual person's tissues. Formula agreement does not establish accuracy for a specific person.

Sources

Frequently asked questions

What is lean body mass (LBM)?
Lean body mass is everything you weigh that is not body fat — muscle, bone, organs, blood, skin, and water. These equations predict lean mass from height and weight; they do not measure those tissues. Some clinical research uses estimated lean mass as a body-size variable, but a calculator result is not a medication dose.
Which LBM formula should I use?
There is no universally best estimate. Boer, James, and Hume were derived from different adult samples. Peters was developed from extracellular fluid-volume relationships in children. Use the equation required by a specific clinical or research protocol rather than selecting the result you prefer.
What is the difference between lean body mass and fat-free mass?
The terms are often used interchangeably in calculators and publications, but definitions can differ by method. This page reports the output of named prediction equations and should not be treated as a direct compartment measurement from DXA or another body-composition method.
Why does age 14 or younger change the result?
Adult Boer, James, and Hume equations were not built for children. The Peters formula estimates extracellular volume from height and weight, then scales that to lean mass, and is intended for ages 13–14 and under. Gender does not enter Peters, but it still changes the adult rows shown underneath.
Can lean body mass be more than 100% of weight?
A predicted value above total body weight is mathematically possible when an equation is used outside the body sizes represented by its source sample. The calculator now labels the implied body-fat result “Not meaningful” instead of displaying a negative percentage.

Related calculators