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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.

US Units

ExampleSample values — edit any field to see your result.

Gender
Age 14 or younger?

Yes lists the Peters pediatric formula first, then the adult formulas for comparison.

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%

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.

Formula

All formulas use weight W in kilograms and height H in centimetres. US entries are converted with 2.2046 pounds per kilogram (the same factor calculator.net uses).

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.

For day-to-day fitness, body-fat percentage is often the more useful number. Use the Body Fat Calculator if you have a tape for neck, waist, and hip, or the Ideal Weight Calculator for a height-based range.

Typical lean-mass share

Typical LBM share of weight
Most adultsabout 60–90%
Men vs womenmen usually a little higher

These bands are averages, not targets. Strength training, age, and how the measurement is taken all move the number.

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.

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. It usually sits around 60–90% of total weight, and men tend to have a higher share than women. Some medicines (especially water-soluble anesthetics) and medical exams use LBM to size a dose.
Which LBM formula should I use?
There is no single best estimate. Boer is widely used in clinical work; James and Hume were derived from different adult samples and sit nearby for most people. This page shows all three so you can see the range. For ages 13–14 and under, Peters is listed first, with the adult formulas kept for comparison.
What is the difference between lean body mass and fat-free mass?
The terms are often used interchangeably, but they are not identical. Lean body mass includes a small amount of essential fat inside organs. Fat-free mass subtracts all fat, including that essential fat. The gap is typically about 2–3% of weight in men and 5–12% in women.
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?
These are population equations, not measurements. For a very tall, light adult they can overshoot body weight and show a negative body-fat percent. Treat that as a sign the formula is outside its comfort zone — a tape estimate or a clinical method such as DEXA is a better next step.

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