What is the calculation for a resting energy requirement (RER)?

December 1, 2025 •

3 min read

The human body at rest burns a significant amount of calories, with some estimates suggesting this can be anywhere from 60% to 75% of total daily energy expenditure. This fundamental energy expenditure is known as the resting energy requirement (RER), and understanding its calculation is a crucial first step in nutritional planning for both people and pets.

Quick Summary

This guide details the standard formulas for calculating the resting energy requirement (RER) for humans and animals. It explains how to use body weight, age, height, and gender to estimate basal energy needs. It covers different formulas and emphasizes that RER serves as a baseline for determining total daily caloric intake.

Key Points

RER vs. TDEE: The Resting Energy Requirement (RER) is the baseline energy for basic bodily functions at rest, while Total Daily Energy Expenditure (TDEE) includes activity and food digestion.
Human RER Calculation: The Mifflin-St. Jeor equation is a modern and accurate formula for humans, using weight, height, age, and gender.
Animal RER Calculation: For pets, the allometric formula, $70 imes ext{kg}^{0.75}$, is generally the most accurate for estimating RER across all body sizes.
Individualized Needs: All RER calculations are estimates and should be adjusted based on an individual's or animal's unique metabolic rate, activity level, and health goals.
From RER to DER: To determine total daily caloric needs, the calculated RER must be multiplied by an appropriate activity factor.
Weight Management Tool: Calculating RER is a critical first step in developing effective weight loss or gain strategies for both humans and pets.

Understanding the Resting Energy Requirement (RER)

The Resting Energy Requirement (RER) is the energy needed for basic functions at rest, such as breathing and circulation. It differs from Total Daily Energy Expenditure (TDEE), which includes energy for activity and digestion. The calculation for a resting energy requirement (RER) is key for nutritional planning and weight management.

Calculating RER for Humans

For humans, RER is similar to Resting Metabolic Rate (RMR) in clinical settings. Common equations like the Mifflin-St. Jeor and Harris-Benedict formulas use weight, height, age, and sex for estimation.

The Mifflin-St. Jeor Equation

The Mifflin-St. Jeor equation is widely used and considered accurate for RMR prediction.

For Men: $(10 imes ext{weight in kg}) + (6.25 imes ext{height in cm}) - (5 imes ext{age in years}) + 5$
For Women: $(10 imes ext{weight in kg}) + (6.25 imes ext{height in cm}) - (5 imes ext{age in years}) - 161$

The Harris-Benedict Equation

While older, the Harris-Benedict equation is still used.

For Men: $88.362 + (13.397 imes ext{weight in kg}) + (4.799 imes ext{height in cm}) - (5.677 imes ext{age in years})$
For Women: $447.593 + (9.247 imes ext{weight in kg}) + (3.098 imes ext{height in cm}) - (4.330 imes ext{age in years})$

Calculating RER for Dogs and Cats

Veterinary medicine uses RER for nutritional management, primarily with formulas based on body weight.

Allometric Formula

This formula is generally considered the most accurate for dogs and cats of various sizes.

RER (kcal/day) = $70 imes ext{(Body Weight in kg)}^{0.75}$

Linear Formula

Simpler but less precise, this formula is suitable for a limited weight range.

RER (kcal/day) = $(30 imes ext{Body Weight in kg}) + 70$

From RER to Daily Energy Requirement (DER)

RER is a baseline. Total daily energy needs (DER) are found by multiplying RER by an activity or maintenance factor. This factor accounts for activity level, life stage, reproductive status, and health conditions.

Common Activity Factors for Humans:

Sedentary (little to no exercise): RER x 1.2
Lightly Active (light exercise 1-3 days/week): RER x 1.375
Moderately Active (moderate exercise 3-5 days/week): RER x 1.55
Very Active (hard exercise 6-7 days/week): RER x 1.725

Common Activity Factors for Pets:

Obesity Prone Dog: RER x 1.4
Weight Loss Dog: RER x 1
Obesity Prone Cat: RER x 1
Weight Loss Cat: RER x 0.8

These factors help personalize energy intake.

Comparison of RER Calculation Methods


Feature	Mifflin-St. Jeor (Humans)	Allometric Formula (Pets)	Linear Formula (Pets)
Application	Widely applicable for human RMR/BMR estimation.	Considered the most accurate for dogs and cats of all sizes.	Applicable for dogs and cats between 2 kg and 45 kg.
Inputs	Weight, Height, Age, Sex	Body Weight	Body Weight
Accuracy	High, generally more modern and precise than Harris-Benedict.	High, especially for animals outside the 2-45 kg range.	Lower accuracy, particularly for very small or large pets.
Formula	Gender-specific algebraic equation.	$70 imes ext{kg}^{0.75}$	$(30 imes ext{kg}) + 70$
Primary Use	Estimating baseline human caloric needs for diet planning.	Establishing a foundational energy requirement for veterinary nutrition.	Quick, rough estimation for animals within a limited weight range.

The Importance of Using a Calculation for a Resting Energy Requirement (RER)

Calculating RER provides a scientific baseline for nutritional needs. It's an estimate, and actual metabolic rates can vary. RER should be adjusted based on individual response and health.

Conclusion

Calculating RER is a fundamental nutritional tool for humans and pets, providing a starting point for dietary planning. Formulas like Mifflin-St. Jeor for humans and the allometric formula for animals estimate baseline calorie needs. Adjustments with activity factors are necessary for total daily needs. Consulting professionals is advised for personalized guidance. Resources like the Pet Nutrition Alliance can be helpful for pet owners.

Frequently Asked Questions

Resting Energy Requirement (RER) and Basal Metabolic Rate (BMR) are very similar concepts that are often used interchangeably, but there is a slight technical difference. BMR measures energy expenditure under strictly controlled, resting conditions (e.g., 12 hours fasted, completely sedentary), while RER is a less restrictive measurement that reflects the body’s energy use at rest after an overnight fast.

The allometric formula, $70 imes ext{kg}^{0.75}$, is generally recommended by veterinary professionals as the most accurate for estimating RER for both dogs and cats of all sizes. The simpler linear formula, $(30 imes ext{kg}) + 70$, can be used but is less accurate, particularly for very small or large animals.

RER only accounts for the energy needed to sustain basic bodily functions at rest. The activity factor is a multiplier used to adjust the RER for additional energy expenditure based on an individual's or animal's daily activity level, life stage, and other factors, to arrive at a total Daily Energy Requirement (DER).

Yes, calculating RER is the foundation for creating a weight loss plan. After determining the RER, you apply a specific weight loss activity factor. For instance, a dog's RER is typically multiplied by 1 for weight loss, and a cat's by 0.8. This provides a target calorie intake to help manage weight safely.

RER calculations are estimates and should be used as a starting point. An individual's actual metabolic rate can vary due to factors like genetics, lean body mass, and age. Individual metabolic rates can differ from the predicted value by as much as 20% to 50%. Regular monitoring of weight and health is essential to fine-tune energy intake.

No, the allometric and linear RER formulas used in veterinary medicine are not sex-specific. However, the activity or maintenance factor (MER) multiplied by the RER to determine total daily calories does vary based on whether a pet is intact or neutered, in addition to other variables.

The Mifflin-St. Jeor equation is generally preferred because it was developed using a more diverse and contemporary population sample than the original Harris-Benedict equation from the early 20th century. This makes it a more accurate predictor of modern RMR values.