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.
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.