Your resting metabolic rate (RMR) is the number of calories your body burns just to stay alive while you’re awake and at rest. For most people, this accounts for 60% to 75% of total daily calorie burn. You can estimate it using a formula that factors in your weight, height, age, and sex, or you can get a more precise reading through a clinical test called indirect calorimetry.
What RMR Actually Measures
RMR represents the energy your body needs in a resting, non-fasting state to power basic functions: breathing, circulating blood, maintaining body temperature, and keeping your brain and organs running. It’s slightly different from basal metabolic rate (BMR), which is measured under stricter conditions, typically first thing in the morning after an overnight fast, 24 hours without exercise, and complete physical and emotional rest. In practice, the two numbers are close enough that most people use them interchangeably, and the formulas below are applied to both.
The Mifflin-St Jeor Equation
The Mifflin-St Jeor equation is the most widely recommended formula for estimating RMR in the general population. It uses metric units, so you’ll need to convert if you’re working in pounds and inches. One pound equals 0.4536 kilograms, and one inch equals 2.54 centimeters.
For men: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
For women: RMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Here’s a worked example. A 35-year-old woman who weighs 150 pounds and stands 5’6″ tall would first convert her stats: 150 lb × 0.4536 = 68 kg, and 66 inches × 2.54 = 167.6 cm. Plugging those in: (10 × 68) + (6.25 × 167.6) − (5 × 35) − 161 = 680 + 1,047.5 − 175 − 161 = roughly 1,392 calories per day.
The Katch-McArdle Formula
If you know your body fat percentage (from a DEXA scan, skinfold calipers, or a reliable scale), the Katch-McArdle formula can give you a more personalized estimate because it’s built around lean body mass rather than total weight. Fat tissue burns very little energy compared to muscle and organs, so two people who weigh the same but carry different amounts of body fat will have meaningfully different metabolic rates.
RMR = 370 + (21.6 × lean body mass in kg)
To find your lean body mass, multiply your total weight in kilograms by your body fat percentage (as a decimal), then subtract that number from your total weight. For example, a person weighing 80 kg at 20% body fat has 80 × 0.20 = 16 kg of fat, so their lean mass is 64 kg. Their RMR would be 370 + (21.6 × 64) = 1,752 calories per day.
This formula is especially useful for people who are very muscular or very lean, since weight-based equations can underestimate their calorie needs. It’s also a better fit for people with obesity, where standard formulas tend to overestimate because they can’t distinguish between metabolically active tissue and stored fat.
The Harris-Benedict Equation
The Harris-Benedict equation is one of the oldest and most studied RMR formulas. In one analysis comparing multiple equations against lab measurements, it produced a mean difference of only about 15 calories per day from actual measured values. However, it only predicted individual RMR within 10% of the true value for roughly 36% of subjects, which highlights an important point: population-level accuracy doesn’t guarantee individual accuracy.
For men: RMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)
For women: RMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)
How Accurate Are These Formulas?
All prediction equations are estimates, and the gap between your calculated number and your actual RMR can be significant. Research evaluating several common formulas found that even the best-performing equations only placed 35% to 64% of individuals within 10% of their measured RMR. That means your true number could easily be 150 to 200 calories higher or lower than what any formula produces.
This matters if you’re using RMR to set a calorie target. Overestimating your metabolic rate can lead to overly aggressive calorie restriction, which makes any diet harder to sustain and increases the risk of losing muscle instead of fat. Underestimating it could leave you eating too much to see the results you’re after, or it could cause you to give up on an approach that would have worked with a small adjustment.
The gold standard for measuring RMR is indirect calorimetry. You breathe into a mask or canopy for 15 to 30 minutes while a machine measures how much oxygen you consume and how much carbon dioxide you produce. Those gas exchange values get plugged into a lab equation to calculate your exact calorie burn. Many dietitian offices, sports performance clinics, and university labs offer this test, typically for $75 to $250.
What Makes Your RMR Higher or Lower
The biggest driver of RMR is how much lean tissue you carry. Muscle burns roughly 4.5 to 7 calories per pound per day at rest. That’s modest on its own, but your internal organs (liver, brain, heart, kidneys) are far more metabolically demanding, burning 15 to 40 times more energy per unit of weight than muscle. Together, lean mass and organ tissue account for most of the variation between individuals.
Age plays a real but often overstated role. RMR drops by approximately 4 calories per year even after adjusting for changes in body composition. Over a decade, that’s only about 40 calories per day. The larger effect of aging is the gradual loss of muscle mass that happens when people become less active, which pulls RMR down further. Staying physically active and maintaining muscle through resistance training can offset much of this decline.
Sex differences in RMR are largely explained by body composition. Men typically carry more muscle and less fat at the same body weight, which is why the Mifflin-St Jeor equation adds 5 for men and subtracts 161 for women. If you use the Katch-McArdle formula (which accounts for lean mass directly), no sex-based adjustment is needed.
Other factors that shift RMR include thyroid function, which regulates your body’s overall metabolic pace; prolonged calorie restriction, which can slow metabolism as the body adapts to less food; and genetics, which account for some of the unexplained variation between people of similar size and age.
Turning Your RMR Into a Daily Calorie Target
RMR tells you what your body burns at complete rest. To estimate your total daily energy expenditure (TDEE), multiply your RMR by an activity factor:
- Sedentary (desk job, little exercise): RMR × 1.2
- Lightly active (light exercise 1 to 3 days per week): RMR × 1.375
- Moderately active (moderate exercise 3 to 5 days per week): RMR × 1.55
- Very active (hard exercise 6 to 7 days per week): RMR × 1.725
- Extremely active (physical job plus intense training): RMR × 1.9
Using the earlier example of a woman with an RMR of 1,392 who exercises moderately three to four days a week, her estimated TDEE would be 1,392 × 1.55 = roughly 2,158 calories per day. That’s the approximate intake needed to maintain her current weight. Eating below that number creates a calorie deficit for weight loss; eating above it supports weight gain.
Keep in mind that both the RMR calculation and the activity multiplier are estimates. Use the number as a starting point, then adjust based on what actually happens over two to four weeks. If your weight stays stable, your estimate is close. If it moves in an unexpected direction, shift your intake by 100 to 200 calories and reassess.