The Katch-McArdle equation is a formula used to calculate your BMR (Basal Metabolic Rate) — the number of calories your body burns at complete rest. Unlike other equations that rely on total body weight, the Katch-McArdle formula uses your Lean Body Mass (LBM) — the weight of your body excluding fat.
BMR = 370 + (21.6 × Lean Body Mass in kg)
This makes it more accurate for people with a known body fat percentage, especially athletes, bodybuilders, or anyone with higher muscle mass relative to their weight.
The Mifflin-St Jeor equation is the most commonly used formula for general populations. It uses weight, height, age, and gender, but does not account for body composition (muscle vs. fat).
BMR (male) = (10 × weight) + (6.25 × height) - (5 × age) + 5
BMR (female) = (10 × weight) + (6.25 × height) - (5 × age) - 161
Key Difference: Mifflin-St Jeor estimates based on total weight, while Katch-McArdle calculates based on lean mass. This means two people with the same weight and age can have different BMRs if their body fat percentages differ significantly.
| Equation | Based On | Accuracy | Best For |
|---|---|---|---|
| Katch-McArdle | Lean Body Mass | High (if body fat is known) | Athletes, Lean Individuals |
| Mifflin-St Jeor | Weight, Height, Age, Gender | High (general population) | Most People |
| Harris-Benedict (Revised) | Weight, Height, Age, Gender | Moderate | Older Adults |
| Cunningham | Lean Body Mass | High | Very Active Athletes |
Athletes and active individuals often have higher muscle mass and lower body fat. Because muscle tissue burns more calories at rest than fat tissue, using total weight can underestimate their metabolic rate.
The Katch-McArdle equation directly accounts for this by using lean body mass, resulting in a more precise BMR calculation for these individuals.
Note: You need a reliable measurement of your body fat percentage (e.g., via DEXA, Bod Pod, or high-quality calipers) for this equation to be effective.