Your body uses energy all the time for essential activities like breathing and digestion. Your metabolism regulates how your body uses energy for these functions.
Basal metabolic rate (BMR) and resting metabolic rate (RMR) both measure the amount of energy —in calories —that your body needs to stay alive and function properly. Many people use the two terms interchangeably, but they have slightly different meanings.
What Is BMR?
Your basal metabolic rate measures the minimum amount of calories that your body needs to perform necessary functions. These functions include:
- Pumping blood throughout your body
- Digesting food
- Keeping a stable body temperature
- Growing hair and skin
- Maintaining levels of different chemicals
Your BMR makes up 70% of the calories you burn every 24 hours. Other ways that your body uses calories include exercising and moving your body in general.
Your weight, height, age, gender, genetics, and other details all play a role in your BMR. The most significant contributor is your weight that doesn’t come from fat, especially your muscles.
How Do You Measure BMR?
Estimate with math. You can estimate your daily BMR with different equations. One of these, the Harris-Benedict equation, is a formula that takes into account your height, weight, age, and gender to find your BMR. You can find BMR calculators online that use these equations.
These calculations can vary in accuracy, and you might get different results from different equations.
Take a test. The most accurate way to calculate your BMR is to get it tested at a lab. You’ll breathe into a special mask called a calorimeter that covers your mouth and/or nose. The mask uses your breath rate to measure the calories you burn.
You’ll need to sleep at the lab overnight to get an accurate BMR measurement. The number of hours you sleep and the temperature of the room can affect your BMR.
You may need to skip exercise and eating for at least 12 hours beforehand. These activities both burn extra calories over time.
What Is RMR?
Your resting metabolic rate is the amount of energy that your body needs to function while at rest. RMR accounts for additional low-effort daily activities on top of basic body functions. These activities include:
- Walking for short periods
- Using the bathroom
- Consuming caffeine
- Sweating or shivering
How Do You Measure RMR?
You can estimate RMR using the same equations you’d use to calculate your BMR. You can also take a lab test with the same type of calorimeter.
The lab test won’t require you to sleep there overnight or restrict eating and exercise beforehand. You’ll likely take the test while staying still in a well-lit room.
Similarities Between RMR and BMR
Your BMR and RMR both capture how many calories your body burns when you’re not exercising. They’re generally around the same number for each person.
Fitness. BMR and RMR can both give you an idea of your overall metabolism. Higher metabolic activity means your body burns more calories each day. Your BMR and RMR both tend to be higher if you’re physically fit.
Total daily energy expenditure. Your total daily energy expenditure, or TDEE, is the total amount of calories you burn each day. Your TDEE consists of calories burned through rest, exercise, and digestion.
Either BMR or RMR can represent the calories you burn at rest in your TDEE.
Differences Between BMR and RMR
Your BMR is a more accurate way to measure your metabolism at complete rest. It’s usually slightly lower than your RMR.
Your RMR is a better number to reference for your daily calorie needs. It more accurately represents the calories you burn in a typical day.
How to Use BMR and RMR to Improve Your Health
Both your BMR and RMR can be useful tools in improving your health. Understanding how your metabolism works can help you tailor your exercise and diet to meet your fitness goals.
Work your muscles. Muscle mass contributes to your BMR or RMR measurement. Most of the energy exchanges in your metabolism take place in your muscles.
Your BMR increases with muscle mass. You can track changes in your BMR throughout a weight-training program. This can help you determine how much muscle you need to burn more calories at rest.
Make a daily calorie plan. To lose weight, you need to eat fewer calories than your body uses in a day. Your BMR makes up a large portion of those daily calories. Knowing your BMR can help you figure out how many calories you should eat to lose or maintain weight.