Cat Food Calculator

Why a cat cannot use a dog food formula

Dogs are scavengers by design and can build several nutrients from plant matter. Cats cannot. Taurine, arachidonic acid and preformed vitamin A have to come from animal tissue, and a cat fed without them can develop heart and eye problems within months. A dog's bowl is not a substitute, and a dog's calorie chart is not a substitute either. The FDA's guide to complete and balanced pet food explains what a cat food has to contain, and the WSAVA global nutrition guidelines lay out the nutrient profile behind those rules.

Both species use the same resting energy formula, 70 times body weight in kilograms raised to the power 0.75, but the multiplier stacked on top is different. A neutered adult dog runs at about 1.6 times resting energy. A neutered adult cat runs at 1.2 times. On the same 10 pounds of body weight, a dog's day lands near 348 calories and a cat's near 261 calories. That gap of 87 calories a day is why a cat fed from a dog's bag gains weight on a portion that looks reasonable.

Cats also evolved to pull most of their water from prey. A cat eating only dry food may drink less than it needs, which is one reason wet food earns a place in the bowl even when the calories work out the same. The number this page gives you is energy, not volume, and those two are far apart once you compare kibble with canned food.

From body weight to calories in two steps

The math has two steps, and neither one is a secret.

Step one, resting energy. Convert the weight to kilograms, raise it to the power 0.75, then multiply by 70. That gives the calories a cat burns while lying still. For a typical indoor cat it covers 60% to 70% of the day.

Step two, the multiplier. Multiply by a factor for life stage and activity. The factor is where most feeding mistakes happen, because it is easy to pick the number for a young active cat when the cat is a middle-aged lap warmer.

The exponent of 0.75 is not arbitrary. Heat loss follows surface area, and surface area grows more slowly than body weight, so a small body burns more calories per pound than a large one. A 6 pound cat needs about 148 calories at rest while a 16 pound cat needs about 310, even though the second cat is less than three times the weight. Feeding by eye, or by the scoop printed on the bag, ignores that curve completely.

Worked example: a 10 pound neutered adult on dry food

Take a 10 pound neutered indoor cat eating a dry food that lists 400 calories per cup.

• 10 pounds is 4.54 kilograms.
• 4.54 raised to 0.75 is 3.11.
• 70 times 3.11 is 218 calories at rest.
• 218 times 1.2 is 261 calories a day.
• 261 divided by 400 calories per cup is 0.65 cups a day.

Split that across two meals and each bowl holds about 0.33 cups, which is a little over five level tablespoons. A level cup of kibble weighs about 4 ounces, so the day's food weighs 2.6 ounces.

Now the cost. At $2.50 a pound, 2.6 ounces of food costs $0.41 a day, or about $12.24 a month. A 12 pound bag holds 192 ounces, so it lasts 74 days for this cat. If the same cat ate from a dog's chart at 348 calories, it would need 0.87 cups a day and the bag would be gone in 55 days, with 2 pounds of extra cat to show for it.

A 14 pound cat on a weight loss plan is the other common case. Resting energy is 280 calories, the 0.8 multiplier brings it to 224 calories, and at 80 calories per 3 ounce can that is 2.8 cans a day, or about 8.4 ounces of food. The bowl looks enormous next to a third of a cup of kibble, and that is the point: water is doing most of the volume work.

Dry food and wet food are not close in calories per ounce

This is the number most people miss. A cup of dry food and a can of wet food can carry the same calories in wildly different amounts of food, because one is 10% water and the other is nearly 80% water.

Calories per ounce is the only unit that lets you compare the two fairly. Kibble runs 85 to 125 calories an ounce. Canned food runs 23 to 35. That is a four to five times difference, and it explains why a cat can eat what looks like a feast of wet food and still lose weight, or eat a modest looking scoop of kibble and gain.

Mixed feeding needs one more step. If you give half the calories as dry and half as wet, work out 130 calories of each, then convert each half separately. Do not split the volume in half, because half a cup of kibble and half a cup of pate are nowhere near the same calories.

Free feeding is how cats get overweight

The single biggest cause of feline obesity is a bowl that never empties. The Association for Pet Obesity Prevention has put the share of US cats above a healthy weight at roughly 60% in its surveys, and free feeding is the habit most often behind it.

The arithmetic is brutal in its simplicity. A single extra average kibble is about 2 calories. Ten extra pieces a day is 20 calories, which is 7,300 calories a year, and a pound of body fat is roughly 3,500 calories. That is 2 pounds a year from a handful of kibble, on a cat that should weigh 10. Over three years the same habit adds six pounds, which on a 150 pound person would be 90 pounds.

Free feeding hides the problem because the bowl is never measured. Two cats in one house make it worse, since the confident cat eats first and the shy cat eats what is left, and neither gets the portion the chart suggests. Timed meals twice a day fix both problems at once. Weigh the food on a kitchen scale in grams for a week, and you will find that a scoop is rarely the size you think it is.

If a cat refuses meals and only grazes, split the daily ration into three or four small servings rather than leaving it out. A puzzle feeder slows the eater who gulps and finishes the other cat's share. What matters is that the total for the day is measured once, in one place, before any of it reaches a bowl.

Kittens, seniors and weight loss change the multiplier

Kittens are not small adults. A kitten under 4 months needs about 2.5 times resting energy, and a kitten between 4 and 6 months needs about 2.0 times, because growth is expensive. Feed a kitten as much as it will eat at each meal until about 6 months, then move to measured portions and watch the body condition rather than the calendar.

Seniors drift the other way. After about 11 years, muscle mass falls and activity drops, so the multiplier comes down to roughly 1.1. A senior that suddenly loses weight on a steady diet is a vet visit, not a portion problem, because thyroid disease and kidney disease both show up that way first.

Weight loss is the case where the formula needs a target, not a current weight. Use the weight the cat should be, not the weight it is, then apply 0.8. A 14 pound cat whose ideal weight is 10 pounds should be fed for 10 pounds, which gives 174 calories rather than 224. That sounds harsh and it is deliberate: a cat should lose 1% to 2% of body weight a week, no faster, because rapid weight loss in cats can trigger fatty liver disease, which is far more dangerous than the extra weight.

Never feed below resting energy for the ideal weight. If the number on screen looks too low to be safe, it probably is, and a vet should set the plan. Pregnant and nursing queens are the other exception: they need two to three times normal intake and should be fed free choice.

Reading the calorie number on the label

Cat food labels are required to state calories, but they state them in whatever unit the maker prefers, and the units are not interchangeable without the cup weight.

You will see three forms. Calories per kilogram is the most common on a can or a bag. Calories per cup is what you need for dry food. Calories per can appears on wet food, sometimes as kcal per can and sometimes as kcal per kg with the can size in small print. Metabolizable energy, written ME, is the usable figure. Gross energy, GE, is higher and not what you feed against.

The conversion is simple: calories per cup equals calories per kilogram times the weight of a cup in ounces times 28.35, divided by 1,000. A cup of kibble weighs between 3.5 and 4.5 ounces depending on the size and shape of the piece, and that alone swings the answer by 20%. Weigh one level cup on a kitchen scale once and use that number, rather than trusting the 8 ounce line on a liquid measuring cup.

The guaranteed analysis on the back cannot give you calories. Crude protein, fat, fiber and moisture are measured by weight, and the carbohydrate figure is whatever is left after the ash and water are subtracted. Two foods with identical protein percentages can differ by 100 calories a cup. Look for the calorie statement, which the FDA requires on pet food labels, and ignore the front of the bag.

When the number on screen is wrong for your cat

Every formula on this page is an estimate built on an average cat. The cat in front of you is the real test, and the test is a hands-on body condition score, not a number on a scale.

Run your hands along the ribs. You should feel them under a thin layer of fat, the way you feel the bones on the back of your hand. A cat with a waist behind the ribs, seen from above, is in good shape. A cat with a straight line from ribs to hips, or a belly that swings, is carrying extra. The 9 point body condition scale used by vets puts 5 at ideal, and most indoor cats sit at 7 or 8.

Weigh the cat every two weeks on a baby scale or by weighing yourself holding the cat and subtracting. If the weight is drifting up, cut the daily portion by 10% and hold it for two weeks before changing anything else. If it is drifting down on a weight loss plan faster than 2% a week, raise the portion. Small changes, two weeks apart, beat a dramatic cut that the cat refuses to tolerate.

Two medical conditions change the answer entirely. An overactive thyroid can raise a cat's calorie burn by 50% or more, so a cat that eats well and still loses weight needs blood work before any diet change. Diabetes, which is often a consequence of long term obesity, needs a vet to set both insulin and food, because the timing of meals matters as much as the amount. For anything beyond a healthy adult on a steady diet, treat this calculator as a starting number to bring to the appointment. The Cornell Feline Health Center has plain language summaries of both conditions.