What is resting energy requirement (RER)?
Updated By PetymFacts checked against official sources on
Quick answer
The resting energy requirement, or RER, is the number of calories a healthy pet needs in a day lying at rest in comfortable surroundings. Vets calculate it from body weight as 70 times the weight in kilograms to the power 0.75, then multiply it by a factor for life stage and neutering to estimate daily food.
Also called RER, resting energy requirement, maintenance energy requirement, MER, dog calorie needs.
Key facts
- RER is the energy needed by a healthy, fed animal at rest in a thermoneutral environment, neither too hot nor too cold. Merck Veterinary Manual
- RER in kcal a day = 70 × (body weight in kg) to the power 0.75, which works for animals of any weight; the simpler 30 × weight in kg + 70 is only for animals between 2 and 45 kg. Merck Veterinary Manual
- Daily maintenance needs are estimated as multiples of RER: 1.8 for intact adult dogs, 1.6 neutered and 1.4 obesity-prone; 1.4, 1.2 and 1.0 for adult cats. Merck Veterinary Manual
- Any given animal may need as much as 30% more or less than the calculated figure, so the result is only a starting point. Merck Veterinary Manual
- A 2025 study of dogs at a Brazilian vet hospital found real energy needs often below the standard estimates, especially in neutered and heavier dogs. Animals (Basel)study
What does the RER number actually mean?
It is the floor: the energy a pet burns just to stay alive at rest. Walking, playing, growing and keeping warm all come on top.
Body weight is raised to the power 0.75 because energy use does not rise in a straight line with size: a 30 kg dog does not need six times what a 5 kg dog needs. That is why the exponential formula works across all sizes, from a Chihuahua to a Great Dane, while the simple linear formula is only reliable between 2 and 45 kg.
On its own, RER suits a pet that really is resting, such as one recovering in a vet hospital. For a healthy pet at home, vets multiply RER by a factor for life stage to get the maintenance energy requirement, or MER, which is the day's food target.
Use the weight your pet should be, not the weight it is, if it is overweight. Your vet can give you that target from a body condition check.
How is RER turned into a daily calorie target?
Multiply RER by the factor for your pet. These are starting points from the Merck Veterinary Manual, not a prescription.
| Multiply RER by | |
|---|---|
| Adult dog, intact Merck Veterinary Manual | 1.8 |
| Adult dog, neutered Merck Veterinary Manual | 1.6 |
| Adult dog, prone to obesity Merck Veterinary Manual | 1.4 |
| Puppy under 4 months Merck Veterinary Manual | 3 |
| Puppy over 4 months Merck Veterinary Manual | 2 |
| Adult cat, intact Merck Veterinary Manual | 1.4 |
| Adult cat, neutered Merck Veterinary Manual | 1.2 |
| Adult cat, prone to obesity Merck Veterinary Manual | 1.0 |
| Kitten Merck Veterinary Manual | 2.5 |
Pets with an illness, pregnant or nursing animals and working dogs need a plan from a vet.
What does the formula give for common weights?
Petym’s working from the official rules, no government publishes a total.
Petym's own working from the formula above, rounded. These are resting figures only, before the life-stage multiplier.
198 kcal
RER for a 4 kg cat or small dog Merck Veterinary Manual
394 kcal
RER for a 10 kg dog Merck Veterinary Manual
662 kcal
RER for a 20 kg dog Merck Veterinary Manual
897 kcal
RER for a 30 kg dog Merck Veterinary Manual
Why does a calculated figure need checking against the pet?
Formulas describe an average animal. Merck notes that an individual may need 30% more or less, and WSAVA's nutrition committee puts the spread at up to 50% either way. A 2025 study of dogs seen at a Brazilian veterinary hospital found many needed fewer calories than the standard inactive-dog estimate, particularly neutered dogs and dogs carrying extra weight, and its authors recommend using the equations together with regular weighing and body condition scoring.
In practice: start with the calculated figure or the food label, weigh your pet every two weeks at first, and adjust portions until it holds an ideal body condition. If a pet seems to need far less than predicted, Merck advises checking for an underlying medical problem such as an underactive thyroid in dogs.
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Questions owners ask
How many calories does my dog need a day?
- Start with RER, which is 70 times your dog's ideal weight in kilograms to the power 0.75, then multiply by the factor for its life stage, for example 1.6 for a neutered adult dog. Treat the result as a starting point, weigh your dog every two weeks and adjust, and ask your vet to set the target.
Is RER the same as the amount on the food bag?
- No. RER is the resting figure before activity. The feeding guide on the bag is based on the expected daily calories of an average pet of that weight, closer to the maintenance figure. Both are starting points; your own pet may need noticeably more or less.
Should I use my pet's current weight or ideal weight?
- For a pet at a healthy weight, use its current weight. For an overweight pet, vets base the calculation on the target weight, often with a lower multiplier, and plan the rate of loss. Ask your vet to set the target weight from a body condition score before cutting food yourself.
Why do vets use the power of 0.75?
- Energy use does not rise in a straight line with body size: bigger animals need fewer calories per kilogram than small ones. Raising weight to the power 0.75 reflects that, which is why the exponential formula works for animals of any size, while the simpler linear formula is only used between 2 and 45 kg.
Keep reading
Related terms
More in nutrition
- BARF dietA BARF diet, short for bones and raw food or biologically appropriate raw food, feeds a dog or cat uncooked meat, organs and bones, sometimes with vegetables. Vets warn that the claimed benefits are not backed by science, while the risks are well documented: germs such as Salmonella and Listeria, bone injuries and unbalanced nutrition.
- Complete and balancedComplete and balanced is a pet food label claim that the food contains every nutrient a dog or cat needs, in the right amounts and ratios, so it can be fed as the whole diet for a stated life stage. Foods without it, labelled complementary or for intermittent feeding, are treats or toppers, not meals.
- Grain-free dietA grain-free diet is pet food made without cereals such as rice, wheat or maize, usually using peas, lentils, other pulses or potatoes instead. Grains are not fillers and most pets digest them well. Since 2018 the US FDA has looked into reports of heart disease, called DCM, in dogs on such foods, without proving a cause.
- Home-cooked dog foodHome-cooked dog food is a dog's main diet made in the family kitchen, such as rice, dal, eggs, chicken and vegetables, instead of a commercial food. It can be healthy if it is complete and balanced, but most generic recipes are not: a UC Davis study found 95% of 200 recipes short of at least one essential nutrient.
- KibbleKibble is dry pet food: dough cooked and shaped under pressure, then dried to about 10% water. It is the cheapest and easiest way to feed a dog or cat a complete diet, keeps at room temperature, and can be measured exactly. Choose one labelled complete and balanced for your pet's life stage.
- TheobromineTheobromine is a bitter natural chemical in cocoa, from the same family as caffeine. Dogs clear it slowly, so a chocolate snack can build up to a poisonous level, causing vomiting, restlessness, a racing heart, tremors and seizures. Cocoa powder and dark chocolate carry the most. If a dog eats chocolate, call a vet straight away.
- Treat allowanceA treat allowance is the share of a pet's daily calories that can come from treats, chews, toppers and table food without unbalancing its diet or causing weight gain. Vets' nutrition guidance puts it at no more than about 10% of the day's calories, with the other 90% from a complete and balanced food.
- Wet foodWet food is canned, pouch or tray pet food, sealed and then heat-sterilised, and roughly 68 to 78% water. It is tasty, filling and adds water to a pet's day, which can help cats with urinary problems, but it costs more per calorie than kibble and spoils quickly once opened, especially in Indian heat.
- XylitolXylitol is a sugar alcohol used to sweeten sugar-free gum, mints, sweets, some nut butters, toothpaste and medicines. In dogs it triggers a large release of insulin, so blood sugar can fall sharply within 10 to 60 minutes, and some dogs go on to liver damage. Any amount eaten is a reason to call a vet straight away.
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Sources
Each source was opened and read on the date shown. How Petym checks its sources
- Merck Veterinary Manual: Nutritional requirements of small animals (full review November 2023, updated September 2024) (opens in a new tab)
- Merck Veterinary Manual: Table: daily maintenance energy requirements for dogs and cats (opens in a new tab)
- WSAVA: Frequently asked questions and myths (Global Nutrition Committee) (opens in a new tab)
- Animals (Basel): Retrospective study of energy requirement recommendations for dogs in a Brazilian veterinary hospital (2013 to 2025), Marchi and others, 2025 (opens in a new tab)