Dog Feeding Calculator

By Wagopedia · Published November 4, 2026 · Built on the RER/DER method published in the Merck Veterinary Manual

The feeding guide printed on a kibble bag is written for an average dog that may not resemble yours. This calculator uses the method veterinarians start from instead: it estimates your dog's resting energy requirement (RER) from body weight, scales it by life stage to get daily energy requirement (DER), and converts the result into cups of the food you actually feed. Enter three things — weight, life stage, and the calories per cup printed on your bag — and you get a daily calorie target and a measured portion.

How it works

Step 1 — Resting energy requirement (RER). RER is the energy a healthy, fed dog uses at rest. The standard formula, published in the Merck Veterinary Manual, is:

The 0.75 exponent is there because metabolism does not scale in a straight line with body weight: a dog twice as heavy does not burn twice the calories at rest.

Step 2 — Daily energy requirement (DER). A resting dog is not a real dog. DER multiplies RER by a life-stage factor drawn from the same veterinary references — growing puppies need multiples of their resting rate, neutered adults need less than intact adults, and a dog on a weight-loss plan is fed at resting rate for its target weight:

Step 3 — Cups per day. Daily calories divided by your food's kcal per cup gives the measured portion. Because foods range from under 300 to over 500 kcal per cup, this step is where bag guides most often mislead: the same "3 cups" can differ by hundreds of calories between brands.

A worked example

Take a 40 lb (18.1 kg) spayed adult dog with typical activity, eating a food labeled 350 kcal per cup:

• RER = 70 × (18.1)^0.75 ≈ 615 kcal/day
• DER = 615 × 1.6 ≈ 985 kcal/day
• Cups = 985 ÷ 350 ≈ 2.8 cups per day — about 1.4 cups per meal if you feed twice a day

Using the result

Treat it as a starting point, then let the dog grade it. The Merck Veterinary Manual notes that any individual dog may need as much as 30% more or less energy than the formula gives for its weight. Feed the calculated amount for two to four weeks, then check body condition: you should be able to feel ribs under a thin fat cover, and see a waist from above and from the side. Gaining? Cut the portion by about 10%. Losing unintentionally? Add about 10%. Recheck after another two weeks.

Count treats in the total. A common veterinary rule of thumb is to keep treats and extras to about 10% or less of daily calories — for the dog in the example above, that is roughly 100 kcal of treats a day, with the food portion reduced to match. Our food and nutrition guides cover which people foods are safe to use as treats and which are dangerous.

Weigh the food if you can. "One cup" scooped by different family members can vary by a quarter cup or more. A kitchen scale removes the argument entirely.

Frequently asked questions

Why does this differ from the feeding guide on the bag?

Bag guides are written for a typical dog of a given weight and tend to be generous — they assume an active, intact adult. The RER/DER calculation adjusts for your dog's actual life stage and neuter status, and then for the real calorie density of your specific food. If the two disagree, start with the calculated amount and adjust by body condition as described above.

How much should I feed a puppy?

Puppies get the highest multipliers here — 3.0 × RER under 4 months and 2.0 × RER from 4 to 12 months — because growth is expensive. Feed a food formulated for growth (it will say so in its AAFCO statement), split the daily amount across three or four meals for young puppies, and expect the right amount to change month to month as the puppy grows. Your veterinarian will track growth at puppy visits; bring the number this calculator gives you and ask whether it still fits.

Does this work for pregnant, nursing, or working dogs?

No. Pregnancy, lactation, and hard physical work raise energy needs well beyond these factors, and the published multipliers for them depend on litter size, stage, and workload. Those are cases for a veterinarian's direct guidance, so this calculator deliberately leaves them out.

What if my dog is overweight but I don't know the target weight?

The weight-loss factor (1.0 × RER) is meant to be calculated at the weight your dog should be, and only a hands-on body-condition assessment can set that target well. Ask your veterinarian for a target weight at your next visit, then run the calculator with that number. Feeding at 1.0 × RER for the current, heavier weight will understate the cut needed; feeding far below it without supervision risks underfeeding nutrients along with calories.