What Is Resting Metabolic Rate (RMR)?
Your Resting Metabolic Rate is the number of calories your body burns at complete rest, the energy required just to keep your heart beating, your lungs breathing, and your cells functioning. An RMR Calculator estimates this foundational number using the Mifflin-St Jeor equation, the most widely accepted predictive formula in modern nutrition science, based on your sex, age, weight, and height. Knowing your RMR is the first step in understanding your total daily energy needs, whether you are planning a weight loss diet, calculating maintenance calories, or setting up a nutrition plan for athletic performance. Toolraxy provides a free, client-side RMR Calculator that gives you this essential metabolic baseline in seconds, with support for both metric and imperial units.
How to Use the RMR Calculator
Select your sex by clicking the Male or Female button.
Enter your age in years.
Enter your weight and select kilograms or pounds.
Enter your height and select centimeters or inches.
Click Calculate. The tool displays your RMR in calories per day, the formula used, and a summary of your weight, height, and age in both metric and imperial units.
How the Tool Works
This RMR Calculator uses the Mifflin-St Jeor equation, which was published in 1990 and has been validated as the most accurate predictive equation for estimating resting metabolic rate in modern populations.
RMR Formulas (Mifflin-St Jeor):
For males:
RMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
For females:
RMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
The result is rounded to the nearest whole number and represents the estimated calories burned in a 24-hour period at complete rest.
Weight and Height Conversion:
The calculator displays your weight and height in both your selected unit and the converted equivalent, providing a clear cross-reference. The formula name is displayed for transparency.
Worked Example
Consider a 30-year-old male who weighs 70 kg (154 lbs) and is 170 cm (67 inches) tall:
Male Mifflin-St Jeor equation: RMR = (10 × 70) + (6.25 × 170) – (5 × 30) + 5
Calculate step by step: 700 + 1,062.5 – 150 + 5 = 1,617.5
Rounded RMR: 1,618 kcal/day.
Display: “RMR (Resting Metabolic Rate): 1,618 kcal/day”
Weight display: “70.0 kg (154.3 lbs)” or “154.0 lbs (69.9 kg)” depending on unit selected.
Height display: “170.0 cm (66.9 in)” or “67.0 in (170.2 cm)” depending on unit selected.
If the same individual were female with the same stats, the equation would be: (10 × 70) + (6.25 × 170) – (5 × 30) – 161 = 700 + 1,062.5 – 150 – 161 = 1,451.5, rounded to 1,452 kcal/day. The approximately 166-calorie difference reflects the Mifflin-St Jeor equation’s accounting for typical sex-based differences in body composition, where females generally have a higher percentage of body fat and lower lean mass at the same total weight.
Benefits of Using This RMR Calculator
Saves time by applying the Mifflin-St Jeor equation instantly.
Reduces manual calculation errors with built-in unit conversions.
Displays results in both metric and imperial units for clarity.
Identifies the formula used for educational transparency.
Free and private, with all calculations running in your browser.
FAQs
How accurate is this RMR calculator?
The Mifflin-St Jeor equation is accurate to within about 10% of measured RMR for most healthy adults. Individual variation depends on body composition, genetics, and health status.
What is the difference between RMR and BMR?
RMR and BMR are often used interchangeably. Technically, BMR is measured under stricter clinical conditions (complete rest, 12-hour fast, specific room temperature). RMR is measured under slightly less strict conditions. The Mifflin-St Jeor equation estimates RMR.
Can I use this calculator to determine my daily calorie needs?
This calculator provides RMR only. Multiply the result by an activity factor to estimate Total Daily Energy Expenditure: 1.2 for sedentary, 1.375 for light activity, 1.55 for moderate, 1.725 for very active, 1.9 for extremely active.
Why does the male formula give a higher RMR than the female formula?
The different coefficients account for average differences in body composition. Males typically have a higher percentage of lean muscle mass and lower body fat percentage, resulting in a higher metabolic rate at the same weight, height, and age.
How often should I recalculate my RMR?
Recalculate whenever your weight changes by 5 kg or more, or every 6 months if your weight is stable. RMR changes as your body composition and weight change.
Does this calculator work for athletes or very muscular individuals?
The Mifflin-St Jeor equation uses total body weight and does not account for high muscle mass directly. Very muscular individuals may have a higher actual RMR than the calculator predicts. For more precise estimates, consider equations that use lean body mass.
Can I share my RMR results?
Yes. Use the Copy button to copy all results, or the Share button to send a summary that includes your RMR and the formula used.
Does this calculator store my personal data?
No. All calculations run entirely in your browser. No personal health data is saved or transmitted.
Is this calculator a substitute for professional nutrition advice?
No. This tool provides estimates for educational purposes. Consult a registered dietitian or healthcare professional for personalized metabolic assessment and nutrition guidance.
What is a normal RMR?
RMR varies widely based on body size, composition, age, and sex. For adults, typical RMR ranges from 1,200 to 2,400 kcal/day. The calculator provides your personalized estimate.
