How to Calculate RMR and BMR Accurately

Over 60-75% of your total daily calorie expenditure is accounted for by your metabolic rate, even before you add any physical activity. Calculating your Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR) provides a powerful baseline for understanding your body's energy needs and managing your weight effectively.

Quick Summary

This guide details the process for calculating your RMR and BMR using established equations. It clarifies the distinctions between the two metrics and explains how to use these figures to determine your daily caloric needs for weight maintenance, loss, or gain.

Key Points

• BMR vs. RMR: BMR is the minimum calories burned at full rest and fasted, while RMR is calories burned at a practical resting state, making RMR a more useful daily metric.

• Mifflin-St Jeor Equation: This is the most recommended formula for calculating RMR, as it is considered more accurate than the older Harris-Benedict method.

• Total Daily Energy Expenditure (TDEE): Your RMR is the basis for calculating your TDEE, which considers your activity level to provide a more complete picture of your daily calorie needs.

• Factors Affecting Metabolism: Age, sex, and body composition significantly influence your metabolic rate, with lean muscle mass being a key factor for a higher metabolism.

• Weight Management Tool: Calculating your metabolic rate and TDEE provides a precise baseline for creating a calorie surplus for weight gain, a deficit for weight loss, or maintenance.

• Personalization is Key: While online calculators offer a great starting point, metabolic rate estimates should be used as guidelines and adjusted based on individual results and goals.

Understanding the Difference Between BMR and RMR

Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) both measure the calories your body burns at rest, but under different conditions. BMR measures the minimum energy needed for vital functions in a strictly fasted and rested state, typically in a clinical setting. RMR is a more practical measurement, accounting for energy burned while awake but at rest, including minor daily activities. RMR is usually 10-20% higher than BMR and is the more accessible figure for most people.

Why Calculating Your Metabolic Rate Matters

Knowing your metabolic rate helps personalize nutrition and training plans. Key factors influencing metabolic rate include body composition (muscle burns more calories than fat), age and sex (metabolism decreases with age, and men generally have higher RMR than women), genetics, and diet and activity level (extreme calorie restriction can slow metabolism).

The Formulas for Calculating Metabolic Rate

The Mifflin-St Jeor and Harris-Benedict equations are common methods for estimating metabolic rate. The Mifflin-St Jeor equation is generally considered more accurate for RMR, while the older Harris-Benedict tends to overestimate.

Mifflin-St Jeor Equation

This formula estimates RMR:

• For men: (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
• For women: (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

Harris-Benedict Equation (Revised)

This revised formula can estimate BMR:

• For men: 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)
• For women: 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)

Using Your Metabolic Rate to Achieve Fitness Goals

To find your Total Daily Energy Expenditure (TDEE), multiply your metabolic rate (RMR is generally used) by an activity factor representing your daily activity level.

Activity Factors:

• Sedentary: little or no exercise (RMR x 1.2)
• Lightly Active: light exercise/sports 1–3 days/week (RMR x 1.375)
• Moderately Active: moderate exercise/sports 3–5 days/week (RMR x 1.55)
• Very Active: hard exercise/sports 6–7 days/week (RMR x 1.725)
• Extra Active: very hard exercise, physical job, or 2x training (RMR x 1.9)

Example Calculation

For a 35-year-old woman, 168 cm, 65 kg, moderately active:

1. Calculate RMR (Mifflin-St Jeor): (10 x 65) + (6.25 x 168) - (5 x 35) - 161 = 1364 kcal/day.
2. Multiply by Activity Factor: 1364 x 1.55 = 2114.2 kcal/day.

Approximately 2114 calories are needed to maintain her weight. Adjusting intake above or below this figure facilitates weight gain or loss.

RMR vs. BMR Calculation Comparison

Feature	BMR (Basal Metabolic Rate)	RMR (Resting Metabolic Rate)
Measurement Condition	Strict, controlled lab environment, post-absorptive (fasted) and fully rested state.	Less restrictive, awake but at rest, post-absorptive but includes minor activity.
Measurement Method	Indirect calorimetry, often in a research facility or metabolic ward.	Indirect calorimetry or estimation via equations like Mifflin-St Jeor.
Accuracy for Daily Use	Less practical, as it excludes low-effort daily energy use.	More practical for daily calorie and weight management planning.
Energy Value	The absolute minimum number of calories needed for basic life functions.	Typically 10-20% higher than BMR due to lower measurement strictness.
Recommended Use	Primarily for clinical research or precise medical evaluation.	The preferred metric for most fitness professionals and individuals.

Conclusion

Calculating RMR and BMR provides valuable insight into your body's caloric needs. RMR is generally more practical for daily use and calculating TDEE, which considers activity level for a complete energy expenditure estimate. Using equations like Mifflin-St Jeor offers a good starting point for setting realistic weight management goals when combined with diet and exercise.

For more detailed information on fitness science, consider resources like the National Academy of Sports Medicine.

Disclaimer: Consult a healthcare professional or registered dietitian for personalized advice, especially with medical conditions.

Frequently Asked Questions

What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is the minimum calories your body needs for basic functions in a completely rested, fasted state. RMR (Resting Metabolic Rate) is the calories burned while at rest but in a more typical daily scenario, making it slightly higher than BMR and more practical for everyday use.

Which is more accurate, BMR or RMR?

While BMR is technically a more stringent measurement, RMR is more practical and provides a more realistic estimate for daily planning because it accounts for minor daily activities like digestion. For most people, RMR is the more useful and accessible metric.

What is the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation is a formula used to estimate Resting Metabolic Rate (RMR) based on an individual's weight, height, age, and sex. It is considered more accurate than the older Harris-Benedict equation for estimating energy expenditure.

Can I increase my metabolic rate?

Yes, you can increase your metabolic rate by building lean muscle mass through resistance training. Muscle tissue burns more calories at rest than fat tissue. Regular exercise and avoiding extreme calorie deficits can also help maintain a healthy metabolism.

How do I calculate my Total Daily Energy Expenditure (TDEE)?

To calculate your TDEE, you first calculate your RMR or BMR and then multiply that figure by an activity factor that corresponds to your lifestyle (e.g., sedentary, moderately active, very active).

Does age affect BMR and RMR?

Yes, both BMR and RMR tend to decrease with age. This is primarily due to a natural loss of lean muscle mass and other hormonal and neurological changes that occur as we get older.

Are online calculators accurate for finding RMR and BMR?

Online calculators provide a convenient estimate based on population averages. While they are a good starting point, they are not 100% accurate and may overestimate energy expenditure. For the most accurate measurement, lab testing is required.