Lean Body Mass Calculator

Height, cm

Weight, kg

Sex

Result

Boer, kg58.1
James, kg59
Hume, kg54.4
Fat mass, kg17
Body fat, %22.6%
Mean of the three, kg57.2

This result is informational only and is not professional advice.

Everything that is not fat

Works out lean body mass with the Boer, James and Hume equations and derives an estimated body fat percentage from it.

Lean body mass is muscle, bone, organs and water — the body without its fat. It matters more than total weight in two situations: dosing drugs that do not distribute into fat, and tracking training, where the scale can sit still while body composition moves.

The Boer, James and Hume equations use only height, weight and sex. That makes them convenient and also limits them: they diverge for anyone whose weight is unusual for their height, and they systematically understate lean mass in muscular athletes.

What this calculator shows

Lean body mass by three accepted equations
Fat mass in kilograms and the estimated fat percentage
The average across the three

What to keep in mind

The equations run on height, weight and sex alone: they cannot tell muscle from bone and cannot see real body composition.
Bioimpedance or DEXA measure it; a formula estimates it. Treat the number as a trend line, not a measurement.

FAQs

What is lean body mass?

Body weight minus fat: muscle, bone, organs and water. Typically 70 to 90 percent of body weight in men and 65 to 85 percent in women.

Which equation should I use?

Boer is the most general-purpose for adults and the one pharmacology usually reaches for. James overestimates in obesity; Hume is the most conservative.

Why do clinicians want lean mass?

Some drugs barely distribute into fat, so dosing by total weight would overshoot. Those are dosed on lean or adjusted body weight instead.

How accurate is the calculated fat percentage?

It carries an error of several percentage points. In muscular people the equations understate lean mass and therefore overstate fat.

Worked example

An average-build man

Input: 175 cm, 75 kg, male

Output: 58.1 kg by Boer, 22.6% fat

Note: James gives 59.0 and Hume 54.4. A spread of nearly five kilograms makes the point: these formulas are useful for tracking change, not for treating any single figure as measured fact.

Useful links

All tools in Health calculators for weight, lab values and training

Lean Body Mass Calculator

Result

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