What is Resting Metabolic Rate (RMR)?

Resting Metabolic Rate (RMR) is the total number of calories your body burns at rest to maintain vital physiological functions such as breathing, circulating blood, regulating body temperature, and conducting cellular respiration. RMR does not include the calories burned during physical activity or food digestion.

How is RMR different from BMR?

BMR (Basal Metabolic Rate) is measured under strict clinical conditions: immediately upon waking, after a 12-hour fast, and in a temperature-controlled dark room. RMR is measured under less restrictive conditions (simply resting quietly) and is typically 5% to 10% higher than BMR, serving as a highly practical baseline for daily energy needs.

Which RMR formula is the most accurate?

For the general population, the Mifflin-St Jeor equation is considered the most reliable modern standard. However, for athletic individuals with high muscle mass and low body fat, the Katch-McArdle formula is superior because it uses Lean Body Mass (LBM) to calculate energy expenditure, acknowledging that muscle tissue is far more metabolically active than fat tissue.

How can I increase my resting metabolism?

The most effective way to permanently increase RMR is to build skeletal muscle mass through progressive resistance training. Skeletal muscle is highly metabolically active, burning approximately 13 kcal per kg per day at complete rest, compared to only 4.5 kcal per kg for fat tissue.

RMR Calculator: Resting Metabolic Rate

Analyze your resting energy expenditure. Compare standard physiological formulas—Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle—to identify your precise metabolic baseline.

Calculate Your RMR

Enter your details to calculate and compare your resting energy expenditure across major physiological models.

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The Physiology of Resting Energy Expenditure

1. Cellular Respiration and Internal Organ Demands

Even when you are lying completely still, your body is performing massive thermodynamic work. Your brain, liver, kidneys, and heart represent less than 6% of your total body weight, yet they account for over 60% of your resting metabolic energy demands. Skeletal muscle at rest accounts for approximately 20-25% of your RMR, while adipose tissue (fat stores) contributes only about 5%. RMR represents the minimum energy required to keep these biological systems functioning.

2. Physiological RMR Formulas Compared

Sports scientists and clinical dietitians utilize three primary mathematical models to estimate RMR:

Mifflin-St Jeor (1990): Developed to reflect modern, less physically active lifestyles. It has been validated as the most accurate predictive formula for general adult populations, showing a high degree of consistency.
Harris-Benedict (Revised by Roza & Shizgal, 1984): An update of the landmark 1919 study. It remains highly respected and is frequently used in clinical settings, though it can slightly overestimate RMR in individuals with high body fat.
Katch-McArdle: This formula bypasses age, gender, height, and total weight, calculating resting expenditure solely from **Lean Body Mass (LBM)**. It is highly recommended for athletes and lifters because it rewards lean muscle tissue and ignores inert fat mass.

Resting Metabolic Formula Matrix

Comparison of mathematical inputs, physiological basis, and target populations:

Formula Name	Required Inputs	Physiological Focus	Optimal Demographic
Mifflin-St Jeor	Weight, Height, Age, Gender	General body mass scaling.	Standard modern sedentary or recreationally active adults.
Revised Harris-Benedict	Weight, Height, Age, Gender	Active cell mass approximation.	Clinical screening; general population baseline.
Katch-McArdle	Lean Body Mass (LBM) / Body Fat %	Active skeletal muscle metabolic weight.	Resistance-trained athletes, bodybuilders, and fitness professionals.

How the Calculation Works

RMR formulas are structured on historical and contemporary clinical validations:

Mifflin et al. (Am J Clin Nutr, 1990): "A new predictive equation for resting energy expenditure in healthy individuals," establishing the standard modern equation.
Roza & Shizgal (Am J Clin Nutr, 1984): "The Harris Benedict equation reevaluated," refining the coefficients to improve modern clinical applicability.

Formula based on the published equation. Methodology reviewed by the Asterisks editorial team. Last content review: June 2025.

Last Updated: June 2026

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Frequently Asked Questions

Physiological Disclaimer: Resting Metabolic Rate calculations are predictive estimations. Real-world RMR can vary by 10% based on genetics, thyroid function, muscle density, hormone levels, and clinical health status. For an absolute measurement, undergo indirect calorimetry in a clinical setting. Full disclaimer →