Daily food portion for a dog or cat

Feeding guides on a bag are written for a weight range, not for an animal, and they are one of the commonest reasons a pet ends up carrying too much. The veterinary route is two steps instead of one: work out the resting energy requirement from body weight, then multiply it by a factor for the life stage and the amount of work the animal actually does. This page does exactly that with the published equation and the published factor tables, and then divides by the energy density printed on your own bag so the answer comes out in grams you can weigh. It is a starting point that a vet adjusts, which is what the sources themselves say it is — it is not a diet, not a weight-loss plan and not advice about a sick animal.

How it is calculated

RER = 70 × BW(kg)^0.75 · DER = RER × factor · grams = DER ÷ (kcal per 100 g) × 100

The exponent is three quarters rather than one because energy use scales with metabolic body weight, so a 4 kg cat needs far more than a tenth of what a 40 kg dog needs. The factor comes from the published daily energy requirement tables — 1.6 for a neutered adult dog, 1.8 intact, 1.2 to 1.4 for a cat, 3 for a dog in moderate work — and where the table gives a range, so does this page rather than picking the middle. The worked example in the source runs a 19 kg dog: 70 × 19^0.75 = 637 kcal/day, times a factor of 3 for moderate work, giving 1911 kcal/day.

Source: Mallory Olson, LVT, VTS, "Energy Calculations: Gauging the Proper Caloric Intake for Patients", Today's Veterinary Nurse, Summer 2022 (peer reviewed) — For dogs and cats of any size, RER (kcal/day) = 70 × body weight (BW [kg])0.75

Questions people ask

Does this replace a vet?

No, and the guidelines are blunt about why. The AAHA nutritional assessment guidelines call the output of exactly this calculation "just population-based starting points for energy requirements, which can vary by 50% in either direction for cats, and by 30% in either direction for dogs". Half again, in either direction, is the difference between a lean cat and a fat one. The number here is where you start; body condition scoring over the following weeks is what settles it, and that is done by someone with hands on the animal. If your pet is ill, pregnant, lactating or losing weight without being asked to, this page is the wrong tool entirely.

Which weight do I type in, the current one or the target?

The ideal weight. The published weight-management guidance calculates the resting requirement from "ideal BW" rather than present weight, and then feeds a percentage of that figure — otherwise an overweight animal is fed to stay overweight. If you do not know the ideal weight, that is itself a reason to have the animal condition-scored rather than to guess: each point on the nine-point body condition scale is about ten percent of body fat, so guessing wrong by two points is guessing wrong by a fifth of the animal.

Why does the answer come out as a range for some choices?

Because the source gives a range for those and inventing a single figure would be more confident than the table it came from. Inactive or obese-prone dogs are 1.2 to 1.4, neutered adult cats 1.2 to 1.4, cats over eleven 1.1 to 1.6, dogs in heavy work 4 to 8. Where the table gives one number — neutered adult dog 1.6, intact 1.8, moderate work 3 — you get one number back. A dog in heavy work has a twofold range because "several hours of physical activity" covers a sheepdog and a sled dog and they do not eat the same.

Where do I find the calories in my food?

On the label. The caloric density of a diet "must be provided by the pet food manufacturer and included on the label", usually as kcal per kilogram and often as kcal per cup as well. Divide kcal/kg by ten to get the kcal per 100 g this page asks for. Do it again every time you change food: wet and dry diets differ enormously in calories per gram, and the source is explicit that "even minor adjustments to the formulation of a diet can have a significant impact on the diet's nutrient profile and caloric density".

What about treats?

They come out of the same budget. The nutrition literature puts the ceiling at ten percent of the day's total calories for everything that is not the main diet — treats, training rewards, the peanut butter in the toy, whatever the tablet is hidden in. A worked example in the source added up an ordinary day of extras for one dog and reached 184 to 209 kcal, which is a third of a small dog's entire allowance. Subtract them from the figure here rather than adding them to it.

What is deliberately missing?

Gestation and lactation. Both are in the same published tables — 1.8 for the first 42 days of a canine pregnancy, 3 for the last 21, and a lactation factor that climbs with the number of puppies — and both come with the instruction to feed free choice, which is the opposite of what a portion calculator does. Putting a gram figure on a nursing bitch would be actively misleading, so this page leaves those rows out and says why instead.

Sources

The documents this page reads its numbers out of, linked so you can check them yourself.

1. Mallory Olson, LVT, VTS, "Energy Calculations: Gauging the Proper Caloric Intake for Patients", Today's Veterinary Nurse, Summer 2022 (peer reviewed) — For dogs and cats of any size, RER (kcal/day) = 70 × body weight (BW [kg])0.75
2. 2014 AAHA Weight Management Guidelines for Dogs and Cats, Journal of the American Animal Hospital Association — "RER in kcal/day = 70 × (ideal BW [kg])0.75"
3. AAHA Nutritional Assessment Guidelines for Dogs and Cats, JAAHA 46 (2010) — "These are just population-based starting points for energy requirements, which can vary by 50% in either direction for cats, and by 30% in either direction for dogs (particularly with the MER)."

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