How much food does a cat need? The answer depends on its weight, its age, and how active it is — and the way to work it out is resting energy requirement, or RER: RER equals 70 times body weight in kilograms to the power 0.75, and daily calories are RER multiplied by a factor for the cat's life stage. This guide is the cat food calculator in words: the formula, the factors, the worked examples, and the cups and grams — so you can work out how much your cat needs without guessing. Every figure is an estimate, not a prescription: individual cats vary, and the vet's advice matters more than the formula. The cat food calculator does the same calculation for your cat's exact weight and stage.
The short version is: weigh your cat, work out its RER, multiply by the factor for its stage, and divide the result by the calories in its food. A neutered adult cat needs about 1.2 times RER, and an intact adult about 1.4 times. A kitten needs about 2.5 times RER. A senior needs less: about 1.2 to 1.4 times RER. The cat calorie calculator guide gives the same method with more worked examples, and the cat food portion calculator guide gives the portion sizes in cups and grams.
The cat food calculator formula
The formula is: RER equals 70 times body weight in kilograms to the power 0.75, and daily calories equal RER multiplied by a factor. The factor is about 1.6 for a neutered adult cat, about 1.8 for an intact adult cat, about 2.0 to 3.0 for an active cat, about 2.5 for a kitten, and about 1.2 to 1.4 for a senior. A lactating cat needs about 2 to 4 times RER, depending on the size of the litter.
| Body weight | Neutered indoor (x1.2) | Intact adult (x1.4) | Active cat (x1.5) | Senior / weight loss (x1.2) |
|---|---|---|---|---|
| 2 kg | 140 | 165 | 175 | 140 |
| 3 kg | 190 | 225 | 240 | 190 |
| 4 kg | 240 | 275 | 295 | 240 |
| 5 kg | 280 | 330 | 350 | 280 |
| 6 kg | 320 | 375 | 405 | 320 |
| 8 kg | 400 | 465 | 500 | 400 |
Read the table from top to bottom and the pattern is clear: a cat's calorie needs rise with weight, but not in proportion — a cat that is twice as heavy does not need twice as many calories, because RER grows with weight to the power 0.75. A 5 kg cat needs about 280 kcal a day as a neutered adult, a 10 kg cat needs about 470 kcal, and a 20 kg cat needs about 795 kcal. The cat food calculator works out the exact figure for any weight and stage.
Worked examples
A 4 kg neutered indoor cat: RER is 70 times 4 to the power 0.75, which is about 198 kcal, and daily calories are 198 times 1.2, which is about 237 kcal a day. A 6 kg neutered indoor cat: RER is about 268 kcal, and daily calories are about 322 kcal a day. A 3 kg neutered indoor cat: RER is about 160 kcal, and daily calories are about 192 kcal a day.
To work out your own cat's needs, weigh it, look up its RER in the table above, multiply by the factor for its stage, and divide the result by the calories in its food — which are printed on the bag or tin, usually as kcal per 100 g or per cup. A typical dry food has about 350 kcal per cup or per 100 g, but the only way to be sure is to check the bag. The how much food should a kitten eat guide gives the calorie tables for young cats, and the senior cat diet guide covers feeding in the senior years.
How much food is that in cups and grams
A typical dry food has about 350 kcal per cup or per 100 g, so a cat that needs 237 kcal a day needs about 0.7 cups or 68 g a day, and a cat that needs 322 kcal a day needs about 0.9 cups or 92 g a day. Those are rough figures, because the calories in a food vary: a food with 400 kcal per cup needs less than a food with 300 kcal per cup, and a wet food has far fewer calories per gram than a dry food, because it is mostly water. Check the bag, and weigh the food — do not guess with a cup, because a cup of kibble can vary by a fifth depending on how full it is.
Split the daily amount into meals: a kitten needs three to four meals a day until about six months, then two meals a day, and an adult cat needs two meals a day. A young animal's stomach is small, so it cannot eat enough in one or two meals to meet its needs, and it needs food little and often. An adult cat can be fed once or twice a day, but twice is better: it keeps the stomach from being empty for too long, and it gives the cat something to look forward to. The how often should you feed a kitten guide gives the feeding schedule, and the how many calories should a cat eat per day guide gives the calorie tables by weight.
When the calculator is wrong
The calculator is wrong when the cat's weight is wrong, when the factor is wrong, or when the food's calories are wrong. Weigh your cat every month, and re-check the amount every two weeks as a young animal grows. Use the right factor: a neutered adult needs less than an intact adult, a senior needs less than a young adult, and a very active cat needs more than a couch potato. Check the bag for the food's calories, and weigh the food — do not guess with a cup.
The calculator is also wrong when the cat is ill, pregnant, nursing, or recovering from surgery: a pregnant cat needs more food in the last weeks, a nursing cat needs much more, and a sick cat may need a special diet. A cat that is losing weight on the calculated amount needs more food, and a cat that is gaining weight needs less — the scales and the body condition score matter more than the formula. The feeding a pregnant cat guide covers feeding in pregnancy, and the feeding a nursing cat guide covers feeding while nursing.
How to use the calculator
Use the calculator to get a starting point, then adjust by the scales and by feel: weigh your cat every month, feel its ribs and waist, and keep it at a body condition score of 4 or 5 out of 9. If your cat is gaining weight, reduce the food by a tenth and re-check in a month. If it is losing weight, increase the food by a tenth and re-check in a month. A cat that is at a healthy weight, eating a measured amount, and exercised every day, is a cat that will live longer and feel better.
Use the calculator to check the bag, too: if the bag says to feed much more than the calculator says, the bag is probably wrong for your cat — feeding guides on bags are often generous, because they are written for active cats and because the maker wants you to buy more food. Trust the calculator, the scales, and your vet, not the bag. The cat food calculator works out the exact figure for any weight and stage, and the cat calorie calculator guide gives the same method with more worked examples.
For related reading, see the cat food calculator, the cat calorie calculator guide, the cat food portion calculator guide, the how much food should a kitten eat guide, the senior cat diet guide, the feeding a pregnant cat guide.
Frequently asked questions
How much food does a cat need?
It depends on its weight, its age, and how active it is. Work out its RER — 70 times body weight in kilograms to the power 0.75 — and multiply by a factor: about 1.2 for a neutered indoor cat, 1.4 for an intact adult, 1.4 to 1.6 for an active cat, 2.5 for a kitten, and 1.1 to 1.4 for a senior. The table above gives the figures by weight.
What is RER?
RER is resting energy requirement: the calories a cat needs at rest, in a comfortable temperature, doing nothing. It is 70 times body weight in kilograms to the power 0.75. Daily calories are RER multiplied by a factor for the cat's life stage — about 1.6 for a neutered adult dog, or 1.2 for a neutered indoor cat.
How much should a 10 kg cat eat?
A 10 kg neutered indoor cat needs about 472 kcal a day, which is about 1.3 cups or 135 g of a typical dry food with about 350 kcal per cup or per 100 g. A 10 kg cat is very large, though — most cats weigh 3 to 6 kg. Check the bag for the food's calories, and weigh the food.
How many meals a day should a cat have?
A kitten needs three to four meals a day until about six months, then two meals a day, and an adult cat needs two meals a day. A young animal's stomach is small, so it cannot eat enough in one or two meals to meet its needs.
Should I trust the feeding guide on the bag?
Not blindly — feeding guides on bags are often generous, because they are written for active cats and because the maker wants you to buy more food. Trust the calculator, the scales, and your vet, not the bag. Weigh your cat every month, and adjust the food by a tenth at a time.
When should I ask a vet about feeding?
Ask your vet if your cat is losing or gaining weight on the calculated amount, if it is pregnant, nursing, ill, or recovering from surgery, or if it has a health condition that affects its diet. A vet can work out the exact amount for your individual cat, and can advise on a special diet if it needs one.
Results on this page are estimates for general information only and are not veterinary advice. If your pet is ill, underweight, overweight, pregnant, or has a health condition, consult your veterinarian before changing diet or care.