How this calculator works
Katch-McArdle uses fat-free mass instead of age and height directly. Body-fat mode subtracts fat mass from weight; the optional Boer estimate is less direct and can add error. The reverse mode returns the lean mass implied by a resting-energy measurement, not a new body-composition measurement. The result is an estimate for information only and is not medical advice.
Formula
BMR (kcal/day) = 370 + 21.6 x lean mass (kg). Lean mass = weight x (1 - body-fat fraction). Boer: male LBM = 0.407W + 0.267H - 19.2; female = 0.252W + 0.473H - 48.3, with H in cm.
Worked example
A lean mass of 60 kg gives 1666 kcal/day. At 80 kg and 25% fat, lean mass is 60 kg and the same energy estimate follows.
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Frequently asked questions
Is lean mass the same as muscle?
No. It also includes organs, bone, blood and other non-fat tissues.
Which input is preferable?
Use a reliable measured fat-free mass if available. Bioimpedance, skinfolds and prediction equations have different errors.
Does this include activity?
No. It estimates resting energy only and is intended for adult comparisons.