Lean Body Mass Calculator
Calculate your lean body mass (LBM) — everything in your body except fat — using the Boer, James, and Hume formulas. Supports metric and imperial units. Also shows fat mass and estimated body fat percentage.
Lean Mass (avg)
60.0 kg
132.4 lbs
Fat Mass
20.0 kg
44.0 lbs
Body Fat %
24.9%
Results by formula
What is lean body mass?
Lean body mass (LBM) is the total mass of everything in your body other than fat — muscles, bones, organs, blood, and water. It is distinct from fat-free mass (FFM), which is identical in concept (some sources use the terms interchangeably, though technically LBM may include a small amount of essential fat in bone marrow and organs).
Knowing your LBM is useful for setting protein intake targets, calculating appropriate medication or supplement doses, and tracking body composition changes during diet or training programmes. It is more meaningful than tracking weight alone, because you can lose fat while gaining muscle — which scales might show as no change or even a small gain.
About the three formulas
Boer (1984): Men: 0.407W + 0.267H − 19.2 | Women: 0.252W + 0.473H − 48.3. Developed from cadaver analysis and considered reliable for most adults.
James (1949): Men: 1.1W − 128(W/H)² | Women: 1.07W − 148(W/H)². One of the earliest formulas, still widely used in medical dosing calculations.
Hume (1966): Men: 0.3281W + 0.3393H − 29.5336 | Women: 0.29569W + 0.41813H − 43.2933. Developed from a large UK dataset.
W = weight in kg, H = height in cm. This calculator shows all three and their average.
Frequently asked questions
Why do the three formulas give different results?
Each formula was derived from a different dataset and population. They can differ by 1–3 kg for the same inputs, particularly at extreme heights or weights. The average of the three formulas is a reasonable middle estimate. For clinical applications (e.g., drug dosing), your healthcare provider will specify which formula to use.
How do I use LBM for protein targets?
Protein recommendations for active individuals are often expressed per kg of lean body mass rather than total body weight — typically 1.6–2.2 g per kg LBM for strength athletes. This avoids over-prescribing protein to individuals with high body fat. Multiply your LBM in kg by your target protein rate (e.g., 2.0 g/kg) to get your daily protein goal in grams.
