Katch-McArdle Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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Calories, macros, and nutrient targets can quickly become abstract. Katch-McArdle Calculator turns the relevant inputs into a practical estimate while keeping the assumptions visible.

What this calculator does

The Katch–McArdle equation estimates resting energy expenditure from lean body mass, making it especially useful when a reasonably reliable lean-mass estimate is available. Nutrition equations are planning tools: real energy and nutrient needs still vary with physiology, goals, health conditions, and the quality of the input data.

How to use it

Enter or select Do you know your lean body mass?, Sex, Weight, Height, and Lean body mass. Use the units offered by the calculator and keep measurements consistent when you plan to compare results over time.

How the calculation works

When lean body mass is entered, the calculator applies BMR = 370 + 21.6 × lean body mass in kilograms. If lean mass is not known, this implementation estimates it from sex, height, and weight with the Boer lean-body-mass equation before applying Katch–McArdle.

Example

For the sample values prefilled in this calculator, the primary result is 1623.9 kcal/day (Katch-McArdle BMR) and Lean body mass is 58.05 kg. This example is there to show how the inputs flow through the implemented equation; replace the sample values with your own measurements before using the result.

How to interpret the result

The output is an estimated resting calorie requirement. Its advantage is that the equation responds to estimated lean mass rather than treating people of the same weight as metabolically identical.

Limitations and notes

Accuracy depends heavily on the lean-mass input or on the accuracy of the Boer estimate used to create it. Hydration, body composition, illness, and individual metabolic variation can shift true resting expenditure from the estimate. For planning, compare the estimate with real-world trends over time instead of reacting to one day. Food-label accuracy, portion estimates, hydration, and activity can all create noise, so modest adjustments are usually more informative than chasing exact calculator precision.