CALCULATOR

Katch-McArdle Calculator

The lean-mass equation. More accurate for lean or trained people, and useless without a body fat percentage.

Result

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BMR–

Daily burn at your activity–

Mifflin-St Jeor–

Harris-Benedict–

Katch-McArdle–

Spread between them–

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The Katch-McArdle equation

Katch-McArdle differs from the other common BMR equations in one important way: it works from lean body mass rather than total bodyweight. Since lean tissue drives most resting energy expenditure and stored fat is comparatively inert, this is mechanistically the more sensible approach.

The catch is that it requires a body fat percentage, and the accuracy of your result depends entirely on the accuracy of that measurement. A tape-based estimate carries roughly three to four percentage points of error, which propagates into the BMR figure.

Where it clearly outperforms the alternatives is at the extremes. For a lean, muscular person, weight-based equations underestimate lean mass and therefore underestimate BMR. For someone carrying high body fat, they overestimate it. Katch-McArdle handles both cases better.

The equation

Katch-McArdleLBM = weight x (1 - body fat percentage / 100)
BMR = 370 + (21.6 x LBM)

Example: 80 kg at 20 percent body fat
LBM = 80 x 0.80 = 64 kg
BMR = 370 + (21.6 x 64) = 1,752 kcal

Why it wins at the extremes

Profile	Weight	Body fat	Katch-McArdle	Mifflin-St Jeor	Difference
Lean athlete	80 kg	10%	1,925 kcal	1,749 kcal	+176
Average	80 kg	20%	1,752 kcal	1,749 kcal	+3
Higher body fat	80 kg	32%	1,546 kcal	1,749 kcal	-203

Three people at identical weight, height and age get the same Mifflin-St Jeor figure, while Katch-McArdle separates them by nearly 400 kcal. That gap is the entire argument for the equation, and also the reason it is useless without a trustworthy body fat measurement.

Getting a usable body fat number

Method	Typical error	Practicality
DEXA	1-2%	Clinic visit, costly
Navy tape method	3-4%	Free, repeatable at home
Skinfold calipers	3-4%	Cheap, needs skill
Bioimpedance scale	4-8%	Convenient, hydration sensitive

A four percentage point error in body fat shifts the Katch-McArdle result by roughly 70 kcal. That is acceptable for a starting estimate and a reason not to treat the output as precise.

Frequently asked questions

What is the Katch-McArdle formula?

BMR = 370 + 21.6 x lean body mass in kg, where lean mass is weight multiplied by one minus body fat as a decimal.

Do I need body fat percentage?

Yes. Without it the equation cannot be used, which is why weight-based formulas remain the default for most people.

Is Katch-McArdle more accurate?

For lean and trained individuals with a reliable body fat measurement, generally yes. For the general population with an estimated body fat figure, the advantage narrows.

How do I measure body fat for this?

The tape-based Navy method is free and reasonably consistent. DEXA is more accurate if you have access to it.

Sources

Katch VL, McArdle WD, Katch FI. Essentials of Exercise Physiology.
Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. American Journal of Clinical Nutrition, 1980.
National Institutes of Health, Office of Dietary Supplements. Nutrient fact sheets. ods.od.nih.gov
NHS. Nutrition and health guidance. nhs.uk
US Departments of Agriculture and Health and Human Services. Dietary Guidelines for Americans, 2025-2030. dietaryguidelines.gov

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General information, not medical advice. Consult a qualified professional before changing your diet, especially with a medical condition.