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Health & Fitness

Lean Body Mass Calculator

Estimate lean body mass (LBM) using the Boer, James, and Hume formulas. Used for medication dosing and body composition tracking.

Boer
61.4 kg
James
62.7 kg
Hume
57.8 kg

What this calculates

Lean body mass (LBM) is everything in your body that isn't fat — muscle, bone, organs, water, connective tissue. It's used clinically for drug dosing (since fat tissue doesn't metabolize most medications) and by athletes tracking body composition changes. Three established formulas estimate LBM from height, weight, and sex.

Formula & how it works

Boer (most common): men LBM = 0.407 × wt(kg) + 0.267 × ht(cm) − 19.2. Women: 0.252 × wt + 0.473 × ht − 48.3. James: men 1.1 × wt − 128 × (wt/ht)². Women 1.07 × wt − 148 × (wt/ht)². Hume: men 0.32810 × wt + 0.33929 × ht − 29.5336. Women 0.29569 × wt + 0.41813 × ht − 43.2933.

Worked example

Man, 80 kg, 180 cm. Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg LBM. Body fat by subtraction: 80 − 61.4 = 18.6 kg, or 23 % BF. Compare to direct body fat methods — they should be in the same ballpark.

Frequently asked questions

Why are there so many formulas?

Each was derived from a different population sample. Boer was a 1984 study; James 1976; Hume 1966. They differ by a few kg for most adults; pick one and stick with it for tracking changes.

What's it used for clinically?

Dosing certain drugs (especially anesthetics, some chemo agents) by LBM rather than total body weight to avoid overdosing obese patients. Hospitals usually use Boer.

Does muscle gain change LBM?

Yes, but slowly. Adding 5 lb of muscle adds 5 lb of LBM. These formulas estimate, though — they don't directly measure muscle. A DEXA scan is more accurate for tracking change.

Should I aim for higher LBM?

Generally yes — more LBM means more strength, more daily calorie burn, better metabolic health. But it has to be earned through training; you can't just diet your LBM up.

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