A cat’s portion follows from two numbers: the calories it needs and the calories in its food. A 4.5 kg neutered adult needs about 70 × 4.5^0.75 × 1.2 = 260 kcal a day; with a dry food of 3,800 kcal per kg, that is 260 ÷ 3,800 × 1,000 = 68 g a day, two meals of 34 g. Enter your cat’s weight, its life stage and the energy printed on the bag, and the calculator gives the daily amount in grams or ounces (and cups, if your bag gives kcal per cup), what a bag lasts and what it costs a month.
Daily calories and dry food by weight
| Cat’s weight | Resting energy (RER) | Neutered adult (× 1.2) | Intact adult (× 1.4) | Dry food, neutered, at 3,800 kcal/kg |
|---|---|---|---|---|
| 2 kg (4.4 lb) | 118 kcal | 141 kcal | 165 kcal | 37 g |
| 3 kg (6.6 lb) | 160 kcal | 191 kcal | 223 kcal | 50 g |
| 4 kg (8.8 lb) | 198 kcal | 238 kcal | 277 kcal | 63 g |
| 5 kg (11 lb) | 234 kcal | 281 kcal | 328 kcal | 74 g |
| 6 kg (13.2 lb) | 268 kcal | 322 kcal | 376 kcal | 85 g |
| 7 kg (15.4 lb) | 301 kcal | 361 kcal | 422 kcal | 95 g |
The need does not grow in step with the weight: a 7 kg cat weighs 3.5 times as much as a 2 kg cat but needs only about 2.6 times the calories, because of the 0.75 power.
Life-stage factors
| Life stage | Factor × RER |
|---|---|
| Adult, spayed or neutered | 1.2 |
| Adult, not neutered | 1.4 |
| Inactive, gains weight easily | 1.0 |
| Weight loss (at the target weight) | 0.8 |
| Kitten up to 4 months | 2.5 |
| Kitten from 4 to 12 months | 2.0 |
The resting-energy formula is the one veterinary nutrition services use; the factors are the commonly used set listed by PetPlace after Hill’s Pet Nutrition. They are starting points: two cats of the same weight can differ a lot.
Making it work
- Read the right number on the bag: “metabolizable energy” or “calorie content”, in kcal/kg or kcal per cup.
- Weigh the food on a kitchen scale for the first weeks; a cup measure varies with the size of the kibble.
- Count the treats and wet food in the optional field so they come off the dry portion.
- Weigh your cat every few weeks and adjust the portion a little if it gains or loses.
Kittens, pregnant or nursing cats and cats with an illness need a vet’s plan. The calculator itself works offline once saved.
Frequently asked questions
How many calories does a cat need a day?
Start from the resting energy, 70 × (weight in kg)^0.75, and multiply by a factor for the life stage: 1.2 for a neutered adult, 1.4 for an intact one. A 4.5 kg neutered cat needs about 260 kcal a day.
How many grams of dry food is that?
Divide the calories by the energy of the food, printed on the bag in kcal per kg, and multiply by 1,000. 260 kcal of a 3,800 kcal/kg food is 68 g a day.
How many cups of dry food should a cat eat?
Many US bags give kcal per cup. Divide the daily calories by that number: at 400 kcal per cup, a cat that needs 260 kcal eats about two thirds of a cup a day.
How do I combine wet and dry food?
Read the calories on the wet food pouch or can and type them as wet food: the calculator subtracts them before working out the dry portion.
How much should an overweight cat eat?
Feed for the target weight your vet suggests, not today's weight, with the weight-loss factor of 0.8. Cats should lose weight slowly; ask your vet before you start.
Sources
- Ohio State University Veterinary Medical Center, Basic calorie calculator
- PetPlace, How to calculate your cat's daily calorie intake (factors after Hill's Pet Nutrition)
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