How much of you isn't fat?
Compare three classical formulas for lean body mass — Boer, James and Hume — plus a fat-mass estimate.
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Lean body mass
Average of 3 formulas
These formulas estimate lean body mass from weight, height and sex alone — no tape measurements needed. Accuracy is in the ±3–4 kg range for healthy adults.
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Frequently asked questions
What is lean body mass?+
Lean body mass is everything in your body that isn't fat — muscle, bones, organs, blood and water. It's typically 75–90% of total bodyweight in healthy adults.
Why does lean body mass matter?+
Protein needs, calorie expenditure and medication doses all scale more accurately with lean mass than total weight. For fitness, LBM is the number you're trying to protect during a fat-loss phase.
Which LBM formula should I trust?+
They're all estimates within ±3–4 kg of the truth for healthy adults. Boer and Hume are the most widely validated for modern populations. We show all three plus their average so you can see the spread.
How is this different from body fat percentage?+
Body fat % uses tape measurements to directly estimate fat. LBM calculators use weight and height regressions that assume average body composition for your sex. Combining both gives you a more complete picture.