Resting Metabolic Rate (RMR) Calculator
Accurate Katch-McArdle Formula based on Body Fat Percentage
Calculation Results
*Calculated using the Katch-McArdle Formula, which is highly accurate for individuals who know their body fat percentage.
How Does Body Fat Affect Your Resting Metabolic Rate?
Your Resting Metabolic Rate (RMR) represents the number of calories your body burns while at rest to maintain basic physiological functions like breathing, circulation, and cell production. Unlike standard BMR calculators that only use age, height, and weight, an RMR calculator with body fat provides a much more personalized result.
The Katch-McArdle Formula Explained
This calculator utilizes the Katch-McArdle Formula. This specific mathematical model is widely considered the gold standard for athletes and fitness enthusiasts because it accounts for Lean Body Mass (LBM). Since muscle tissue is significantly more metabolically active than fat tissue, two people of the same weight but different body fat percentages will have vastly different caloric needs.
Formula: RMR = 370 + (21.6 × Lean Body Mass in kg)
Why Lean Mass Matters
Muscle is "expensive" for the body to maintain. It requires constant energy even when you are sleeping. By inputting your body fat percentage, the calculator determines your lean weight (muscles, bones, organs) and applies the metabolic multiplier only to the tissue that actively burns energy. This prevents overestimating caloric needs for those with higher body fat and underestimating for those with significant muscle mass.
Realistic Examples
- Example A: An 80kg individual with 15% body fat has 68kg of lean mass. Their RMR would be approximately 1,838 calories.
- Example B: An 80kg individual with 30% body fat has 56kg of lean mass. Their RMR would be approximately 1,579 calories.
Despite being the same weight, Example A burns nearly 260 more calories per day just staying alive, thanks to a higher muscle-to-fat ratio.
How to Use These Results
Once you have your RMR, the Total Daily Energy Expenditure (TDEE) is calculated by multiplying your RMR by your activity level. To lose weight, you should aim for a caloric intake between your RMR and TDEE. To gain muscle, you generally need to consume calories slightly above your TDEE while performing resistance training.