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Pet obesity is a huge problem in the United States, and one of the reasons behind this is that we simply feed our pets too much. Food is love, and pet parents like to fill their pets’ bowls and shower them with treats. Often, pet owners don’t actually know how many calories their pets should ideally receive on a daily basis. To make matters worse, feeding guides or charts on pet food labels are only rough, basic guides; they do not take into account complex factors like the pet’s activity level or body condition. Learning how to calculate your pet’s caloric needs will help you be more accurate when measuring out your pet’s food.
Please note: This is a guide for healthy adult animals only. Talk to your pet’s usual veterinarian if they are still growing, pregnant or lactating, overweight, underweight, or if they have a disease.
The formula
The basis of this calculation lies in a formula that separates different aspects of an animal’s physique. It has many moving parts and is fairly complex, but when it is broken down, it becomes easy to understand just how much goes into determining your pet’s calorie requirements.
MER stands for maintenance energy requirement. It is equal to the number of kilocalories (kcal) your pet needs to consume per day, taking into account factors like signalment, lifestyle, and body condition score.
NOTE: kilocalories (kcal) is the same as Calories (Cal) used in human nutrition.
The basic formula for MER is:
TIP: Write down each part of the equation as you read through the following steps.
Step 1
Convert pounds to kilograms
Before tackling the equation, you must first convert your pet’s body weight in pounds to kilograms. Using kilograms is standard practice in veterinary medicine, and it makes the calculation less complex.
The calculation for pounds to kilograms is:
TIP: Round to 2 decimal places for greatest accuracy
Example #1: Raven weighs 9.5 lb
9.5 lb ÷ 2.2 = 4.32 kg
Example #2: Bruin weighs 65 lb
65 lb ÷ 2.2 = 29.55 kg
Step 2
RER
The first part of the MER equation is the RER, or resting energy requirement. RER is the kilocalories (kcal) your pet needs each day to perform basic processes like breathing and sleeping.
The calculation for RER is:
NOTE: bw = body weight in kilograms
Example #1: Raven
RER= 70 x (4.32)0.75
RER = 210 kcal/day
Example #2: Bruin
RER = 70 x (29.55)0.75
RER = 887 kcal/day
Step 3
Signalment
Signalment is the term used to describe a pet’s species and reproductive status. Cats and dogs have different energy requirements, and intact pets require more energy than spayed or castrated pets.
TIP: The “factor” is the number you will input into the MER equation. Write down which factor best matches your pet’s signalment.
Step 4
Activity level
Exercise plays a huge role in how many calories your pet needs to consume. Pets who are fairly inactive require much less energy than pets who are consistently exercising.
Step 5
Body condition score
To learn how to body condition score your pet, see How to body condition score.
Body condition score is another key factor when determining how much a pet should consume. Overconditioned (overweight) pets need to eat fewer calories so they can lose some weight. Underconditioned (underweight) pets need to eat more calories so they can put on muscle and fat.
NOTE: If your pet is underweight, talk to their usual veterinarian before following this formula. There might be a disease process happening that could affect their nutrition requirements.
NOTE: If your pet is overweight, talk to their usual veterinarian before following this formula. Rapidly decreasing calorie intake may be detrimental to your pet’s health.
Step 6
Putting it all together
If you’ve been keeping track of your pet’s factors, you can now input them into the MER equation and calculate how many kilocalories they need per day.
Step 7
Converting kilocalories to cups
Look on the pet food label to find how many kilocalories are in a cup of food.
The equation for calculating how many cups your pet requires per day is:
Example #1: Raven
Her food is 427kcal/cup
202 kcal/day ÷ 427 kcal/cup = 0.47 cups/day
Example #2: Bruin
His food is 475 kcal/cup
1,703 kcal/day ÷ 475 kcal/cup = 3.59 cups/day
As you can see, these measurements are not very easy to measure out in a standard pet food scoop. Therefore, converting your pet’s food to grams is a much more accurate and preferred method (see How to accurately measure your pet’s food for more information).
Converting kilocalories to grams
Look on the pet food label or call the pet food manufacturer to find out how many kilocalories are in a gram of food, OR how many grams are in a cup of food (see How to pick a pet food, part 1 for more information).
There are two options for calculating how many grams your pet requires per day:
Option A example: Raven
Her food is 3,800 kcal/kg (listed on bag)
convert to kcal/g
→ 3,800 kcal/kg ÷ 1,000 g = 3.8 kcal/g
202 kcal/day ÷ 3.8 kcal/g = 53 g/day
Option B example: Bruin
His food is 475 kcal/cup, with 112 g/cup
(1,703 kcal/day ÷ 475 kcal/cup) x 112 g/cup = 402 g/day
Step 8
Separating into meals
Most pets eat more than once per day, so you will now have to calculate how many grams they get per meal. Simply divide the total grams per day by the number of meals per day.
Example #1: Raven → 3 meals per day
53 g/day ÷ 3 meals/day = 17.66 g/meal
→ 18g in the morning, 18g in the evening, 17g at night
Example #2: Bruin → 2 meals per day
402 g/day ÷ 2 meals/day = 201 g/meal
→ 201g in the morning, 201g at night
Final notes
Make sure you take calories from treats into consideration when feeding your pet. Visit Treats, table scraps, and food toppers for more information!
All pets are different. Some pets do great on this formula, while others may need to be adjusted to maintain a good weight and body condition. Weigh your pet and take a body condition score before starting this new regimen. After 2 weeks of changing your pet’s caloric intake, weigh them again and reassess their body condition. Reassess your pet and adjust each part of this formula as needed if and when their weight and body condition score change.
Example #1: You want your pet to stay the same, and. . .
Pet stays the same → great! Keep doing what you’re doing.
Pet loses weight/ body condition → increase caloric intake.
Pet gains weight/ body condition → decrease caloric intake.
Example #2: You want your pet to lose weight, and. . .
Pet loses weight/ body condition → great! Readjust the formula accordingly every 2 weeks.
Pet stays the same or gains weight/ body condition → uh-oh! Talk to their usual veterinarian about special weight loss diets and exercise plans.
Example #3: You want your pet to gain weight, and. . .
Pet gains weight/ body condition → great! Readjust the formula accordingly every 2 weeks.
Pet stays the same or loses weight/ body condition → uh-oh! Talk to their usual veterinarian to rule out disease processes.
Resources
Nutrition and Disease Management for Veterinary Technicians and Nurses
PNA: “Calorie Calculator for Cats”
PNA: “Calorie Calculator for Dogs”
Ohio State University: “Basic Calorie Calculator”
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