How the cat food calculator works

Cat food amounts are calculated the same way as dog food amounts — from the resting energy requirement, RER = 70 × (body weight in kilograms)^0.75 — but the activity factors are different, because cats are not small dogs. A neutered adult cat has a factor of about 1.2, an intact adult about 1.4, a kitten under four months about 2.5, a kitten from four months to adulthood about 2.0, an inactive or senior cat about 1.0, and a cat on a vet-guided weight-loss plan about 0.8. For a typical 4.5-kilogram neutered adult cat, the RER is about 218 kcal a day and the daily need is about 262 kcal — roughly two-thirds of a cup of dry food, or one small can of wet food plus a little dry. The calculator shows the RER, the factor, the daily calories and the equivalent in cups and grams, so you can see every step of the working.

Cats are obligate carnivores, which changes what "food" means. A dog can get by on a diet with a substantial carbohydrate content; a cat cannot. Cats need animal protein for essential amino acids such as taurine and arginine, and they need arachidonic acid, a fat found only in animal tissue. That is why the calculator is about amounts, not recipes: the amount is a number, but the food itself must be a complete and balanced cat food, labelled as such, and never dog food. Dog food lacks the taurine and vitamin A levels a cat needs, and a cat fed dog food for weeks will develop serious deficiencies. The same applies to homemade diets, which need a vet-formulated recipe and a supplement — see the homemade diet portion calculator for the amount, and your vet for the recipe.

Wet food, dry food, and the water question

Wet food is about seventy to eighty percent water, while dry food is about ten percent. That means a cat eating wet food gets a large part of its daily water from its food and drinks less from the bowl — which is normal and healthy, and one reason vets often recommend wet food for cats prone to urinary problems. The calculator assumes dry food when it converts calories to cups, so if you feed wet food, use the calorie figure and divide by the kcal per can on the label instead. Many owners feed a mix: a measured amount of dry food left out for grazing plus one wet meal a day. That can work, but the total must still add up to the daily calorie figure — the most common cause of cat obesity is free-feeding dry food all day on top of wet meals, so that the cat eats two full rations without anyone noticing.

What affects the result

Weight is the main input, and for cats it is often wrong: owners routinely underestimate their cat's weight by a kilogram or more, because cats are hard to weigh and because a long-haired cat looks bigger than it is. Weigh your cat on bathroom scales by holding it and subtracting your own weight, or ask your vet to weigh it at the next visit. Neutering matters a great deal — neutered cats need about twenty to thirty percent fewer calories than intact cats, and the risk of weight gain is highest in the months after neutering. Age matters: kittens need two to two and a half times their RER, while seniors need about their RER and no more. Activity matters less for cats than for dogs, because most cats regulate their own activity, but an indoor cat that never plays needs fewer calories than one that roams and hunts.

Common mistakes

Free-feeding dry food is the biggest mistake — a bowl that is always full means the cat eats whenever it is bored, and most cats will overeat. The second is treating the bag guide as a prescription: like dog food guides, cat food guides are generous ranges for the average cat. The third is forgetting treats and table scraps, which should stay under ten percent of daily calories — a few treats a day can be a quarter of a small cat's intake. The fourth is cutting food sharply to make a fat cat lose weight: rapid weight loss in cats can cause hepatic lipidosis, or fatty liver disease, which is life-threatening. A cat should never lose more than about one percent of its body weight per week, and any weight-loss plan must be vet-supervised.

When to see a vet

See your vet before changing your cat's diet if it is overweight, has kidney disease, diabetes, urinary problems, hyperthyroidism, or is a kitten, pregnant or nursing. Cats with kidney disease need a different diet, not just less food, and cats with diabetes need a consistent, measured feeding routine to match their insulin. See a vet promptly if your cat stops eating for more than a day — a cat that does not eat for twenty-four to forty-eight hours is at risk of fatty liver disease, and that is an emergency, not a hunger strike. For the calorie figure behind the food amount, use the cat calorie calculator; to check whether your cat's weight is healthy, the cat ideal weight calculator; and for mealtimes, the feeding schedule generator.