Free tool · Nutrition

Katch-McArdle calculator: resting calories from lean mass

Short answer

The Katch-McArdle equation estimates resting calories from fat-free mass alone: 370 + 21.6 × fat-free mass in kg, the general equation Cunningham proposed in 1991. An 80 kg (176 lb) person at 20% body fat has 64 kg of fat-free mass and an estimated 1,750 kcal a day at rest. It needs a body fat estimate, but ignores age, sex and height.

Last reviewed 28 October 20263 published sourcesNot medical advice

Reps keeps track of this for you on iPhone, iPad and Apple Watch.

Get Reps free

Katch-McArdle calculator

Resting calories from fat-free mass: 370 + 21.6 × fat-free mass in kg (Cunningham, 1991).

Units
kg
%

From a scan, smart scale or the body fat calculator.

Enter your weight and body fat percentage.

Runs entirely in your browser. Nothing you type is saved or sent anywhere.

Resting calories by fat-free mass
Fat-free massResting calories
40 kg (88 lb)1,230 kcal/day
50 kg (110 lb)1,450 kcal/day
60 kg (132 lb)1,670 kcal/day
70 kg (154 lb)1,880 kcal/day
80 kg (176 lb)2,100 kcal/day
90 kg (198 lb)2,310 kcal/day
370 + 21.6 × fat-free mass (Cunningham, 1991), rounded to the nearest 10 kcal.

The equation and its name

Cunningham pooled studies of body composition and resting energy expenditure and proposed one general equation: resting energy = 370 + 21.6 × fat-free mass in kg. Fat-free mass explained 65–90% of the variation in resting energy in the studies he reviewed (Cunningham, 1991).

The same equation is widely called the Katch-McArdle equation; a 2025 weight-loss trial, for example, set its participants' calorie targets from "Katch-McArdle" resting energy, written as 370 + 21.6 × lean body mass (Tang et al., 2025).

Fat-free mass comes from your weight and body fat percentage. The ACSM, Academy of Nutrition and Dietetics and Dietitians of Canada position statement works the same step through: 60 kg at 20% body fat is 48.0 kg of fat-free mass (Thomas, Erdman & Burke, 2016).

From resting calories to a full day

Resting calories leave out everything you do. Compare this estimate with the Mifflin–St Jeor figure in the BMR calculator, get a body fat estimate from the body fat calculator, and add activity with the TDEE calculator.

Eat for the body you are building

Reps logs meals by photo, voice or text with a full macro breakdown, next to the training and recovery your Apple Watch records.

Download Reps on the App StoreNutrition in Reps

Free to download · iPhone, iPad and Apple Watch

Common questions

What is the Katch-McArdle formula?

Resting energy (kcal/day) = 370 + 21.6 × fat-free mass (kg). Cunningham proposed it in a 1991 review as a general prediction equation that explained 65–90% of the variation in resting energy expenditure across the studies he pooled. Fat-free mass is weight × (1 − body fat %).

Why is it called Katch-McArdle if Cunningham proposed it?

The equation is published as Cunningham's (1991), but researchers and fitness sites often call it the Katch-McArdle equation, after the exercise physiology textbook by McArdle, Katch and Katch that presents it. Both names refer to the same 370 + 21.6 × fat-free mass formula.

Is Katch-McArdle more accurate than Mifflin–St Jeor?

It can suit people whose build is unusual for their weight, such as very muscular athletes, because it works from lean mass rather than total weight. But it is only as good as your body fat number, and home estimates from a smart scale or tape measure are rough. If you don't know your body fat, Mifflin–St Jeor in the BMR calculator is the safer choice.

Sources

Figures on this page were checked against these publications on 28 October 2026.

  1. Cunningham JJ. Body composition as a determinant of energy expenditure: a synthetic review and a proposed general prediction equation. American Journal of Clinical Nutrition. 1991;54(6):963–969. doi.org/10.1093/ajcn/54.6.963
  2. Tang M, Wang J, Xiang Y, Xu R. Metabolic adaptation fluctuates with different prediction equations: a secondary analysis based on a weight-loss clinical trial. Frontiers in Nutrition. 2025;12:1543263. doi.org/10.3389/fnut.2025.1543263
  3. Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine joint position statement: nutrition and athletic performance. Medicine & Science in Sports & Exercise. 2016;48(3):543–568. doi.org/10.1249/MSS.0000000000000852

More nutrition tools

See every free tool →