How Much to Feed a Cat: The Actual Math, Not the Bag's Guess

Sixty-one percent of the cats US veterinary professionals assessed in the latest Pet Obesity Prevention survey were overweight or obese, and a 1.34-million-cat dataset from primary-care clinics shows the same curve peaking in middle age. Portions are where that starts, and the arithmetic behind a correct portion is public. This page shows it, sourced at every step, because "follow the bag" is precisely how most of those cats got there.

The formula your vet uses

Veterinary nutrition starts from the resting energy requirement, RER: the calories a cat burns doing nothing in a comfortable room. Per the Merck Veterinary Manual, RER = 70 x (body weight in kg)^0.75. Daily need is RER multiplied by a lifestyle factor:

Worked example, the same cat as our eggs article: a 10 lb (4.5 kg) neutered adult. RER is 70 x 4.5^0.75, about 216 kcal; times 1.2 gives roughly 260 kcal a day. WSAVA's quick-reference table brackets the same cat at 240 to 270 kcal, so the two independent methods agree. WSAVA also publishes a one-step shortcut (100 x kg^0.67 for a lean adult) that lands slightly higher, around 275 kcal for this cat, which is worth knowing for one reason: different reputable calculators use different formulas, so two "official" answers 20 kcal apart are both right. Every source says the same thing about all of them: this is a starting point, adjusted on how the individual cat's weight actually responds.

To turn calories into grams, use the calorie statement on the label. In the US that number is mandatory on every cat food and treat under AAFCO labeling rules; in Australia, the industry standard makes an energy statement optional, so an Australian label may simply not carry one, and the manufacturer's website or your vet fills the gap. Wet food is roughly 70 to 80% water, which is why the "how many pouches" answer looks so much bigger than the dry-grams answer for the same calories.

The check that beats the scale: body condition

Vets score cats by feel on a 9-point body condition scale, and both WSAVA and AAHA use 5 as ideal: ribs felt under a slight fat covering, a visible waist behind the ribs, minimal belly pad. The stakes of each point are quantified: per AAHA, every point above 5 is roughly 10% overweight. The full nine points, and what an ideal-condition cat of your cat's build actually weighs, are in our cat weight chart. You can run the feel test weekly at home in ten seconds, ribs, waist, belly, and it catches drift long before the bathroom scale does. Most owners never do: in PDSA's UK survey, 84% did not know their cat's body condition score, and only 12% took portion advice from a vet, while about a fifth portioned by "common sense".

Why the bag overfeeds your cat specifically

Cornell states the mechanism plainly: label feeding guides are built for the average cat, so if yours expends less energy than average, the bag overfeeds it. An indoor, neutered cat is below average on both counts: neutering measurably lowers energy expenditure (which is why it gets its own, lower multiplier above), and an indoor lifestyle is itself a documented obesity risk. AAHA's own guideline says the quiet part: in an ideal world, owners run the calculation rather than relying on package guidelines.

The cost of drifting heavy is not cosmetic. As our diabetes article carries, obese cats run up to four times the diabetes risk of ideal-weight cats; Cornell's follow-up work adds seven times the lameness risk and twice the risk of dying in middle age. One definitional footnote, since institutions differ: Cornell calls obesity 20% or more above normal weight, the obesity-prevention association uses 30%; same direction, different lines.

How often, and in what shape

Cornell's schedule by age: three meals a day until six months, twice daily from six months to a year, once or twice daily for adults, seniors unchanged unless the vet says otherwise.

But the strongest guidance on meal SHAPE comes from the feline practitioners' 2018 consensus: cats are solitary hunters of small prey, built to eat little and often, alone. One or two big meals at a shared bowl "can lead to inactivity and even distress, often resulting in overconsumption and obesity", their words. Their recommendation is to split the daily allowance into multiple small meals across the 24 hours, with puzzle feeders where possible. The same statement notes modern kibble is palatable and fast to eat, which feeds overeating. Free-feeding dry food works for some cats; for others, per Cornell, it is the straight road to weight gain, and the honest test is your cat's body condition, checked monthly.

The water angle, briefly

A 2026 review of 32 studies found cats on wet diets take in more total water than cats on dry, and only wet-fed groups reliably reached the intake that keeps urine dilute. Cats fed exclusively dry food carried a 2.6-times higher risk of lower urinary tract disease than cats on a mixed diet in the underlying studies. Portioning and hydration are the same decision more often than the two aisles suggest; the urinary side lives in our urinary article.

If your cat needs to lose weight, the one rule that is not negotiable

Never crash-diet a cat. A cat losing weight too fast, or abruptly not eating, can develop hepatic lipidosis, a potentially life-threatening liver condition; that is Cornell's warning, and it is why feline weight loss is a supervised project, not a smaller scoop starting tomorrow. The published, vet-supervised pace is 1 to 2% of body weight a week, on a therapeutic weight-loss diet when restriction is significant, because those diets are fortified so fewer calories does not mean missing nutrients. A cat that simply stops eating is its own urgent story: our not-eating article carries the thresholds. And the standing rule: if something is wrong with your cat, call your vet; out of hours, an emergency clinic.

Treats fit inside the math

WSAVA, AAHA and the feline practitioners' consensus all put the same ceiling on everything outside the main diet: 10% of daily calories, counted within the allowance rather than on top of it. (Cornell's page has recently said "10 to 15 percent"; we keep the 10% figure the other three institutions state unanimously.) For the worked-example cat, that is about 26 kcal a day of treat budget, and the eggs article shows what it buys. The reason is nutrient balance, not just calories: past 10%, the treats start displacing the complete food that carries the actual nutrition.

What to take away

• The starting formula is 70 x (weight in kg)^0.75 kcal a day, times 1.2 if neutered (Merck): about 260 kcal for a typical 10 lb (4.5 kg) neutered adult.
• The label's kcal line, not cups or pouches, is the number that transfers between brands; for many 4.5 kg cats the target lands around three 85 g pouches a day.
• Free-feeding dry food works for some cats and quietly fattens others: the monthly rib-and-waist check is the test, and measured meals win once weight drifts.
• Cats are built for many small meals: splitting the same total into more portions, ideally through puzzle feeders, changes begging without adding a calorie.
• A diet is safe at 1 to 2% of body weight a week, with a vet: rapid loss or sudden fasting can trigger hepatic lipidosis, a serious liver disease.