How Many Calories Should a Cat Eat? The Arithmetic, and Where It Stops

Why the requirement does not double when the cat does

Metabolic rate scales with body mass to roughly the three-quarter power, not to the first power. This is Kleiber's law, and it holds across an enormous range of animals: a big body has proportionally less surface to lose heat through and a metabolism that runs slower per unit of tissue. The consequence for feeding is direct. Two to the power of 0.75 is 1.68, so doubling a cat's weight raises its resting requirement by 68 per cent, not by 100. The calculator implements exactly this: 70 × weight in kilograms, raised to 0.75.

The practical form of the same fact is that calories per kilo of cat fall as the cat gets bigger. At 2 kg a kitten needs about 71 kcal per kilo per day on the neutered-indoor factor; at 4.5 kg an adult needs 58; at 9 kg it needs 48. Anyone who works out a portion by scaling from a friend's cat, or from a chart with two weight bands and a straight line between them, will be systematically wrong — too much for the heavy cat, too little for the light one. And the cat it overfeeds is the one that most needs it not to be overfed.

The multiplier is where the real spread lives

The resting figure is a physiological number; the daily figure is a judgement, and the tool makes it with a single multiplier chosen from nine options. Neutered and indoors is 1.2. Intact adult is 1.4. Active or with outdoor access is 1.6. Senior, over eleven, is 1.1. Weight loss and overweight share a factor of 1.0. Kittens under four months and lactating queens are both 2.5, kittens from four to twelve months and pregnant queens both 2.0. On a 10 lb cat that is a range from 218 to 545 kcal a day depending purely on which line you pick — two and a half times, on the same animal.

Two of these deserve attention because they are commonly got wrong. Neutering lowers the requirement — the tool puts a neutered indoor cat 17 per cent below an intact adult of the same weight — and it does so at the moment when many cats are also given free access to food for the first time, which is why the months after neutering are when so many cats put on the weight they never lose. And indoor against outdoor is worth a third: 261 against 348 kcal on a 10 lb cat. A cat that stops going out has not become a smaller cat, but it has become a cat whose ration should change.

The pack is not lying, it is answering a different question

A feeding guide on a pouch or a bag prints one portion for a weight band. It cannot ask whether the cat is neutered, whether it goes out, whether it is eleven or three, or whether it already weighs more than it should — and those questions move the answer by a third in either direction. So the pack's number cannot be right for most of the cats in its band; it is a starting point aimed at the middle of a population. Since most owned adult cats are neutered and many live indoors, which is the lowest adult multiplier on the tool's list, a band figure aimed at the population middle will read high for that group. That is a reasoning from the tool's own factors rather than a published finding, and it is worth checking against your own cat's weight over a month rather than taking on faith.

The one number on the pack you should trust is the energy density, because it is a measured property of that food. It is the bridge between a calorie figure and a portion you can weigh. The calculator can do the conversion for you, but only in one direction: it offers a field for kilocalories per cup, which is a North American measure — the field is labelled in cups in all six of its languages. In markets where food is labelled per hundred grams, do it by hand: a 4.5 kg neutered indoor cat needs 260 kcal a day, so on a dry food at 400 kcal per 100 g that is 65 g, and on a wet food at 85 kcal per 100 g it is 305 g.

The weight-loss line, and why it is the vet's to draw

This is the point at which the arithmetic has to stop, and the tool now stops cleanly. Its weight-loss option used to apply its factor to the weight you typed in — the cat's current weight — where a weight-loss ration is computed from the weight the cat ought to be. A 15 lb cat that should be 10 lb got 295 kcal instead of 218, thirty-five per cent more than the setting was supposed to deliver, and in the one direction that defeats the purpose of choosing it. There is now a target-weight field, and the panel says which weight the answer was computed on. The target itself is not the tool's to invent: your vet sets it, because feline weight loss driven too hard causes hepatic lipidosis, and that is fatal.

But the reason to hand this over to a vet is not the arithmetic — it is what happens if you get it wrong in the other direction. Cornell's Feline Health Center defines feline obesity as twenty per cent or more above normal weight, says probably half the cats seen in clinics are overweight, and puts a safe rate of loss at perhaps one or two per cent of body weight per week, under supervision. The reason for that ceiling is hepatic lipidosis. The Merck Veterinary Manual calls it the most common and potentially lethal acquired liver disease of cats, and among the things that trigger it, it lists a change of diet made to initiate weight loss. A cat that suddenly eats much less mobilises fat faster than its liver can process, and the liver fills with it. That is why the target and the rate belong to someone who has weighed the animal, scored its body condition and can watch it week by week.

Frequently asked questions

Why does my cat, at twice the weight of my neighbour's, not need twice the food?

Because energy use rises with mass to the power 0.75, not to the power 1. Doubling the mass multiplies the requirement by 1.68, so a 20 lb cat needs 439 kcal a day where a 10 lb cat needs 261 — 68 per cent more, not 100. There is a second reason worth separating out: if the heavier cat is heavier because it is overweight rather than because it is a bigger frame, then part of that extra mass is fat, which is metabolically quiet, and feeding it as though it were muscle is exactly how the weight stays on.

My cat is overweight — can I just pick the weight-loss option?

Select it and give it the target weight your vet set. It multiplies by 1.0 — the resting requirement, no activity allowance — and applies that to the target rather than to the weight the cat has now, which is what a weight-loss ration means. A 15 lb cat aiming at 10 lb gets 218 kcal from it, where the same factor on the current weight would give 295. There is still no control over the rate of loss, and there should not be: that is a clinical decision, and going too fast is the thing that kills.

How much difference does neutering really make?

On this tool's factors, a neutered indoor cat sits at 1.2 × resting and an intact adult at 1.4 — seventeen per cent apart, which on a 10 lb cat is 261 kcal against 305, or about 44 kcal a day. Forty-four kilocalories sounds trivial and it is roughly a sixth of the ration, every day, for years. What makes it matter more than the arithmetic suggests is timing: neutering usually coincides with the cat settling down, with the end of the growth phase, and often with a move to free feeding. Three changes that all point the same way arrive at once, and the ration usually does not change with them.

The pack says more than the calculator. Which one do I follow?

Follow the cat. Both numbers are estimates for a population, and the only measurement that settles it is your own animal's weight over four to six weeks on a fixed, weighed ration. Weigh the food rather than scooping it, keep the amount identical every day, weigh the cat at the start and again at the end, and read the direction. If the weight is stable and the body condition is right, the ration is right whatever either number said. That is also the answer to the underlying question, because a calorie figure is only ever a place to start measuring from.

How do I turn a calorie figure into a portion I can actually measure?

Divide the daily calories by the food's energy density, which the pack has to state. The calculator offers a field for kilocalories per cup, which is the North American convention; a 10 lb neutered indoor cat needing 261 kcal on a 400 kcal-per-cup dry food comes out at 0.65 cups a day, or 0.33 per meal on two meals. Wherever food is labelled per hundred grams, work in grams: the same cat on a food at 400 kcal per 100 g needs 65 g a day, and on a wet food at 85 kcal per 100 g it needs 305 g. Weigh it once on a kitchen scale, find the container that holds that amount, and use the container after that — the reason to weigh is that a scoop of dry food varies by twenty per cent depending on how it is filled.