What is RMR?
Resting Metabolic Rate (RMR) is the number of calories your body burns while at complete rest to keep its basic systems running: breathing, circulating blood, keeping your organs working, and maintaining body temperature. It represents the energy you would spend over a day if you did nothing but rest quietly.
RMR is reported in kilocalories per day (kcal/day) and is the single largest component of most people’s daily energy use. Knowing it gives you a sensible baseline for planning how much to eat to lose, maintain, or gain weight.
How does it work?
This calculator estimates RMR with the Mifflin-St Jeor equation, published in 1990 and widely regarded as one of the most reliable predictive formulas for resting energy expenditure in healthy adults. It takes four inputs: your sex, weight (converted to kilograms), height (converted to centimeters), and age in years. A constant term differs between men and women to reflect typical differences in lean body mass.
In everyday use the terms RMR and BMR are often treated as interchangeable. Strictly, BMR is measured under stricter overnight-fasted, fully-rested laboratory conditions, so a measured RMR usually sits a few percent higher. Because the Mifflin-St Jeor equation is the standard predictive formula for both, this calculator returns the same estimate you would get from a BMR calculator.
Formula
With weight in kilograms, height in centimeters, and age in years:
-
For men:
-
For women:
The only difference between the two is the final constant: men add 5, women subtract 161. Whatever units you enter for weight and height are converted to kilograms and centimeters before the equation is applied.
Examples
Example 1: RMR for a man
Suppose a man weighs 80 kilograms, is 180 centimeters tall, and is 30 years old.
His estimated RMR is approximately 1780 kcal/day.
Example 2: RMR for a woman
Suppose a woman weighs 80 kilograms, is 180 centimeters tall, and is 30 years old.
Her estimated RMR is approximately 1614 kcal/day. The 166 kcal gap between the two examples comes entirely from the different constant term.
Notes
- RMR is not your total daily calorie need. To estimate how much you actually burn, multiply your RMR by an activity factor that reflects how active you are throughout the day.
- Estimates vary between individuals. Two people with identical sex, height, weight, and age can have genuinely different resting metabolism because of muscle mass, genetics, hormones, and other factors.
- Designed for adults. Predictive equations like Mifflin-St Jeor are validated for adults and are less reliable for children, athletes with very high muscle mass, or people with certain medical conditions.
FAQ
What is the difference between RMR and BMR?
They measure almost the same thing: the energy your body uses at rest. BMR is measured under stricter fasted and fully-rested conditions, so a measured RMR usually reads a few percent higher. Both are commonly estimated with the Mifflin-St Jeor equation, which is why this calculator and a BMR calculator return the same figure.
Why does the formula differ for men and women?
On average, men carry more lean muscle mass than women of the same height and weight, and muscle burns more energy at rest. The different constants (+5 versus -161) adjust the estimate to reflect this typical difference in body composition.
How accurate is the estimate?
For most healthy adults, the Mifflin-St Jeor equation lands within roughly 10% of measured resting energy expenditure, which is why dietitians and researchers commonly prefer it over older formulas. It remains an estimate, not a measurement.
Should I eat exactly my RMR in calories?
No. Eating only your RMR would generally be too few calories because it ignores the energy you spend on daily activity and exercise. Use RMR as a baseline and add an activity factor to estimate a more realistic intake.