Katch–McArdle Calculator & Formula
Estimates basal metabolic rate (BMR) from your lean body mass — so it's the one BMR formula that accounts for body composition, and the one that needs a body-fat %.
Katch–McArdle works from lean mass — weight minus fat — because muscle burns energy and fat barely does. That makes it sharp for lean or muscular people, where weight-based formulas misfire, but it's only as good as the body-fat number you give it. WIMSTA runs it beside Mifflin–St Jeor, Harris–Benedict and WHO/FAO as a range.
At 70 kg and 25% fat, your lean mass is 52.5 kg, so Katch–McArdle gives 1504 kcal/day. Slide body fat up or down: Katch–McArdle moves, Mifflin stays put — because Mifflin never sees composition. That is the formula's strength and its catch: it is only as good as the body-fat number you feed it. The full calculator shows it beside Mifflin, Harris–Benedict and WHO/FAO as a range.
The name hides its real source
The "Katch–McArdle" BMR equation (370 + 21.6 × lean mass) is a textbook formula, popularised in Katch & McArdle's Exercise Physiology. There is no separate Katch–McArdle experiment behind it: term for term it is Cunningham's 1991 equation (Am J Clin Nutr 54(6):963–969). We cite the original and show it once — listing "Katch–McArdle" and "Cunningham" as two formulas would be the same estimate counted twice, which would make a range look falsely tight.
That's the difference between a real range and a padded one: it only counts methods derived independently of each other.
Sharp for
Lean, muscular or athletic people with a measured body-fat % (DEXA, calipers, hydrostatic) — it sees the muscle the others miss.
Weak when
Your body-fat % is a guess — the error flows straight in, and Mifflin–St Jeor becomes the safer choice. Not for pregnancy or under-18s.
BMR is step one. You want calories.
Katch–McArdle, Mifflin–St Jeor, Harris–Benedict and WHO/FAO rarely agree to the calorie. The calculator shows the honest range and turns it into your maintenance calories (TDEE).
Open the calorie calculatorCunningham (popularised by Katch & McArdle) — Am J Clin Nutr 54(6):963–969 (1991), lean body mass vs measured RMR. The 370 + 21.6·LBM coefficients implemented in our engine match Cunningham 1991 and are covered by the test suite.
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FAQ
What is the Katch–McArdle formula?
It estimates basal metabolic rate from lean body mass: BMR = 370 + 21.6 × lean mass (kg), where lean mass is your weight minus your fat. Because it works from lean tissue — the metabolically active part — it needs a body-fat % as an input, unlike Mifflin–St Jeor or Harris–Benedict.
Is Katch–McArdle more accurate than Mifflin–St Jeor?
For lean and muscular people with a reliably measured body-fat %, yes — keying off lean mass removes the bias that weight-based formulas have. But if your body-fat % is just a guess, that error flows straight into the result, and Mifflin is the safer default.
Is Katch–McArdle the same as the Cunningham equation?
Effectively yes. The "Katch–McArdle" BMR formula (370 + 21.6 × lean mass) is identical to Cunningham's 1991 equation; it is a textbook formula popularised under the Katch–McArdle name, with Cunningham 1991 as the underlying source. We show it once and cite the original.
How do I turn Katch–McArdle BMR into daily calories?
Multiply BMR by an activity factor — about 1.2 sedentary up to ~1.9 very active — to get maintenance calories (TDEE). The calculator does this and shows the range across every BMR equation.
How every formula is sourced: the method page.