Katch-McArdle Calculator
Use this Katch-McArdle calculator to estimate your resting calorie burn from lean mass.
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Field Notes that go deeper
The science behind the Katch-McArdle calculator
Show the formulas, method and sources
The Katch-McArdle equation estimates your resting energy use from lean mass instead of total weight. The tool turns your weight and body fat percentage into lean mass, then applies the equation. If you add an activity level, it also estimates maintenance calories.
Formulas
Lean mass
Lean mass (kg) = weight (kg) x (1 - body fat % / 100)
Katch-McArdle
BMR = 370 + 21.6 x lean mass (kg)
Maintenance (when you pick an activity level)
TDEE = BMR x activity factor (1.2, 1.375, 1.55, 1.725 or 1.9)
How it works, step by step
- First, the calculator converts your weight to kilograms and subtracts the fat share you entered.
- Then it applies the Katch-McArdle equation to the lean mass.
- If you chose an activity level, it multiplies the result by the matching factor.
- Finally, it rounds the results to the nearest 10 calories.
Worked example
A person who weighs 70 kg with 20% body fat has 56 kg of lean mass. The equation gives 370 + 21.6 x 56 = 1,579.6, which rounds to 1,580 calories a day. With moderate exercise the factor is 1.55, so maintenance comes to about 2,450.
Accuracy and limits
In their 1990 sample, Mifflin and colleagues found that fat-free mass was the best single predictor of resting burn. That is why an equation built on lean mass can help when you know your body composition.
A 2021 study of 620 healthy women compared several equations with measured resting energy. Katch-McArdle landed within 10% of the measured value for 39.5% of them, the highest share of any equation tested. However, it overestimated by about 163 calories a day on average.
Because the result follows your body fat number, any error in that number carries through. A 5-point difference in body fat at 70 kg shifts lean mass by 3.5 kg, which changes the result by about 76 calories.
- The accuracy study covered healthy women, so results for men, athletes or older adults may differ.
- The equation ignores age, sex and height, because it uses lean mass alone.
- Before you rely on the result, compare it with two to three weeks of real weight data.
Sources
- Molina-Luque R, Carrasco-Marin F, Marquez-Urrizola C, et al. Accuracy of the resting energy expenditure estimation equations for healthy women. Nutrients. 2021;13(2):345. Used for: The Katch-McArdle equation as written and how it compared with measured resting energy.
- Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. Used for: The Mifflin-St Jeor equation and the 498 adults it came from.
Sources and math last reviewed: .
Questions people ask
What is the difference between Katch-McArdle and Mifflin-St Jeor?
Mifflin-St Jeor uses weight, height, age and sex. Katch-McArdle uses lean mass alone. If you know your body fat, it can reflect muscle better, but it then depends on that estimate.
How do I find my lean mass?
Lean mass is your weight minus your fat mass. A scan, calipers or a tape-measure estimate can give you the fat share, and the lean body mass calculator works out the rest.
Is Katch-McArdle more accurate than other equations?
It can be, though it is not always. In a 2021 study of healthy women it came within 10% of measured resting energy most often among the equations tested, yet it still overestimated by about 163 calories a day. Accuracy depends on how good your body fat number is.
Does it replace my TDEE?
No. It estimates resting burn only. If you add an activity level, the tool shows maintenance calories, and the TDEE calculator offers the same step from height, weight and age.
Which body fat number should I use?
Use the most reliable number you have. If you only have an estimate, try a few nearby values to see how far the result moves.
These calculators give general estimates for adults and are not medical advice. For decisions about your own health, talk with a doctor or a registered dietitian. How we write and check things