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Lean Body Mass Calculator
Compare Boer, James and Hume lean-mass estimates, or calculate fat-free mass from body-fat percentage.
Lean Body Mass Calculator: Compare Boer, James and Hume lean-mass estimates, or calculate fat-free mass from body-fat percentage. Runs 100% locally in your browser with zero server file uploads.
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- Health & sport tools
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- In your browser
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- Free · no sign-up
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- Ready to use
Runs entirely in your browser
Lean mass includes water, organs and bone as well as muscle. These adult equations can be unreliable at high body weights, especially James. Do not use these estimates for medicine dosing.
Estimates for adults only. Not suitable for pregnancy, breastfeeding or a personalised treatment plan. Activity factors are broad assumptions; actual needs vary.
Height and weight equations
With kg and cm, Boer: men 0.407w + 0.267h − 19.2; women 0.252w + 0.473h − 48.3. James: men 1.1w − 128(w/h)²; women 1.07w − 148(w/h)². Comparison study: https://pmc.ncbi.nlm.nih.gov/articles/PMC6110034/
Hume: men 0.32810w + 0.33929h − 29.5336; women 0.29569w + 0.41813h − 43.2933. Formula comparison: https://pmc.ncbi.nlm.nih.gov/articles/PMC5079277/
Measured body fat
Fat-free mass = weight × (1 − body-fat percentage / 100). These adult equations are population models, not direct composition measurements. Hume original study: https://pmc.ncbi.nlm.nih.gov/articles/PMC473290/ .
How to use it
- Enter weight in kilograms, height in centimetres and sex.
- Add a measured body-fat percentage if available.
- Compare the estimates and read the limits of height-weight formulas.
Privacy & limitations
Your inputs stay in this browser. Nothing you enter is uploaded or saved.
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Frequently asked questions
Is lean mass the same as muscle mass?
No. It also includes water, bones and organs. Fat-free mass calculated from a body-fat percentage depends on the accuracy of that measurement.
Why can James look implausible?
Its squared weight-to-height term becomes unreliable at very high body weights. Values outside zero to total body weight are marked outside the useful range. None of these results should set medicine doses.
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