Calculate your lean body mass (LBM) — muscle, bone, organs, and water — using the Boer, James, and body fat percentage methods. Includes Fat-Free Mass Index (FFMI).
Your Measurements
Enter height, weight, sex, and optionally body fat %
Lean Body Mass
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FFMI
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Boer Formula
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James Formula
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From Body Fat %
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Fat Mass
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Lean Body Mass
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Fat Mass
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Boer LBM
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James LBM
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FFMI
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Normalized FFMI
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Enter your measurements
Add body fat % for the most accurate LBM calculation.
FFMI Range (Men)
FFMI
Category
<18
Below average
18–20
Average
20–22
Above average
22–25
Excellent (advanced training)
25–27
Near genetic maximum
>27
Likely performance-enhanced
Frequently Asked Questions
What is Lean Body Mass?
Lean Body Mass (LBM) = Total weight − Fat mass. It includes everything except body fat: muscles, bones, organs, skin, and water. LBM is important because it drives your metabolic rate.
What is FFMI?
Fat-Free Mass Index (FFMI) = LBM ÷ height². It normalizes lean mass for height, similar to BMI but for lean tissue only. It is the best metric for comparing muscularity between people of different heights.
Why are there different LBM formulas?
Different formulas were derived from different population studies. The Boer formula is accurate for most people. The James formula is also widely used. If you know your body fat percentage, using LBM = weight × (1 − BF%) gives the most direct result.