Cats are small, which makes feeding errors easy: an extra half-cup of kibble a week is the feline equivalent of a daily donut. Roughly half of indoor cats are overweight, and portions measured by scoop instead of by numbers are the main reason. Here's the formula vets use, a table by weight, and the can-count and fresh-food math for whatever you're pouring.
The veterinary approach starts from the resting energy requirement: RER = 70 x (weight in kg)^0.75. That 0.75 exponent is Kleiber's law, and it's why a 20 lb cat burns about 2.8 times what a 5 lb cat burns, not four times. The same equation runs our dog food calculator; only the factors change.
The standard feline factors, from the charts veterinary nutrition centers use:
| Weight | RER (kcal) | Neutered indoor (x1.2) | Intact (x1.4) | Kitten (x2.5) |
|---|---|---|---|---|
| 5 lb | 129 | 155 | 181 | 323 |
| 8 lb | 184 | 221 | 258 | 460 |
| 10 lb | 218 | 261 | 305 | 544 |
| 12 lb | 249 | 299 | 349 | 624 |
| 15 lb | 295 | 354 | 413 | 737 |
| 20 lb | 366 | 439 | 512 | 915 |
Worked example: a 10 lb tabby weighs 4.5 kg. RER = 70 x 4.5^0.75 = 218 kcal. She's spayed and indoor, so 218 x 1.2 = 261 kcal a day. That's the entire calculation. Run your own cat's numbers, including treats and meals-per-day splitting, in the cat food calculator.
The label is the source of truth: kcal per can for wet, kcal per cup for dry. Typical ranges:
| Format | Typical kcal | For a 261-kcal cat |
|---|---|---|
| 3-oz can (wet) | 70-100 | 2.6-3.7 cans/day |
| 5.5-oz can (wet) | 130-200 | 1.3-2.0 cans/day |
| Dry kibble | 300-450/cup | 0.6-0.9 cups/day |
| Fresh (Smalls, JustFoodForCats, Raised Right, Darwin's) | 28-40/oz | 6.5-9.3 oz/day |
Two traps hide in that table. First, cans vary wildly: 70 kcal and 100 kcal look like the same can and differ by 40%. Second, dry food is calorie-dense; the same daily calories that need 2.7 cans of wet fit in 0.75 cups of kibble, so the switch from wet to dry without recalculating is a classic weight-gain event.
Enter weight, life stage, and your label's kcal per can, cup, or ounce. See daily kcal, portions per day, and per-meal amounts.
Cat Food Calculator →Fresh and gently cooked brands (Smalls, JustFoodForCats, Raised Right, Darwin's, and others) cluster around 28-40 kcal per ounce, roughly 1.0-1.4 kcal per gram, and ship portioned packets sized near a day's food for common weights. At 35 kcal/oz, our 261-kcal tabby eats 7.5 oz a day. Every packet prints its kcal, so divide daily calories by the packet figure and you're done. Fresh food's main practical edge for cats is moisture and portion control, not magic: the calorie math is identical.
Factor 1.0, calculated at the target weight. A 15 lb cat whose lean weight is 11 lb gets RER at 11 lb = 234 kcal a day, even though maintaining a neutered 15 lb cat takes 354 kcal. That gap is the diet.
Two cat-specific cautions. Weight loss must be slow, about 0.5-1% of body weight per week, because cats that stop eating or diet too hard can develop hepatic lipidosis, a liver emergency. And a vet should confirm the target weight first; a 15 lb Maine Coon and a 15 lb domestic shorthair are very different patients. Weigh the cat every two weeks on the same scale.
A cat's natural pattern is 8-10 small meals a day, the hunting rhythm. The modern substitutes: measured meals two to three times daily, or a puzzle feeder that meters the same total into slow pursuit. Free feeding works only for the minority of cats who self-regulate; for the rest, a bottomless bowl is the direct path back to this article. If you track your own intake the way we do in the calorie calculator, the principle transfers exactly: total calories in, portions measured, adjustments in 10% steps.
The final scoreboard is the cat, not the formula. You should feel ribs under a thin fat layer, see a waist from above, and find minimal belly pouch from the side. That's a body condition score of 5 out of 9. Any big change, a weight-loss plan, or a kitten of a large breed should involve your vet; everything else, the calculator plus a scale handles.
Divide daily calories by the kcal per can on the label. A 10 lb neutered indoor cat needs about 261 kcal a day; on a typical 95-kcal 3-oz can that's 2.7 cans, split across two or three meals. The same cat on a 5.5-oz can at 165 kcal gets 1.6 cans a day. The label's kcal figure beats any breed-based chart, because cans vary from 70 to 200 kcal.
By weight, not by scoop. A 10 lb neutered cat eating a 350 kcal/cup kibble gets 261 kcal, or 0.75 cups a day, which is only about 1.7 oz by weight. A level 8-oz measuring cup of dense kibble can hold 450 kcal, so a 'cup a day' habit overshoots by 70 percent. A $12 kitchen scale makes overfeeding almost impossible.
Fresh brands like Smalls, JustFoodForCats, Raised Right, and Darwin's run about 28-40 kcal per ounce (1.0-1.4 kcal/g). A 261-kcal cat needs 7-9 oz a day, at 35 kcal/oz about 7.5 oz. Start from your cat's RER x factor, divide by the packet's kcal, and adjust 10% after two weeks based on body condition.