How to use the cat calorie calculator
- Enter your cat's weight (use the ideal weight for a weight-loss plan).
- Choose the life stage that fits best.
- Optional: add the food's kcal per kg to see grams a day.
- Press Calculate.
Worked example
Milo, a neutered adult cat weighing 4 kg, eating a food that lists 3,800 kcal/kg.
- Weight
- 4 kg
- Life stage
- Neutered/spayed adult
- Food energy (kcal/kg on the bag) — optional
- 3800
- Resting energy (RER)
- 198 kcal/day
- Factor used
- 1.2 × RER
- Food per day
- 63 g
Example values are illustrative; this result is produced by the same calculator above.
How we calculate it
Sources: NRC · Merck Veterinary Manual · WSAVA Global Nutrition Guidelines
Reference table
| Weight | kcal/day |
|---|---|
| 2 kg / 4 lb | 141 |
| 3 kg / 7 lb | 191 |
| 4 kg / 9 lb | 238 |
| 5 kg / 11 lb | 281 |
| 6 kg / 13 lb | 322 |
| 7 kg / 15 lb | 361 |
Understanding your result
The calculator starts from your cat's resting energy requirement (RER), the energy a healthy cat needs just to stay alive at rest: 70 × body weight in kilograms raised to the power 0.75. A 4 kg cat has an RER of about 198 kcal a day.
It then multiplies RER by a factor for life stage. A neutered adult cat uses 1.2, an intact adult 1.4 and an inactive or obesity-prone cat 1.0. For a weight-loss plan the factor is 0.8, applied to the RER of your cat's ideal weight, not its current weight.
The result is maintenance energy (MER), a starting point rather than a prescription. Weigh your cat every few weeks, feel the ribs and waist, and adjust the amount in small steps. If you add the food's kcal per kilogram, the calculator also converts the calories into grams a day.
Cats are small, so small errors matter: 20 kcal is roughly 8% of a neutered 4 kg cat's day. That is why measuring food in grams on a kitchen scale beats guessing with a scoop.
Common mistakes
- Entering the weight the cat should be instead of the weight it is, unless you are following a vet's weight-loss plan.
- Forgetting treats, toppers and tastes of human food; they all count toward the daily calories.
- Copying the kcal per kilogram from a different product or from the dry-matter column of the label.
- Cutting calories sharply to speed up weight loss. Cats must lose weight slowly and crash diets can cause serious liver disease.
- Using this adult calculator for kittens, pregnant or nursing cats; use the Kitten Food Calculator or ask your vet.
Good to know
- Energy needs are not a straight line with weight, which is why the formula uses a power of 0.75.
- Wet and dry foods have very different calories per gram, so portions by volume or by eye are easy to get wrong. The Cat Food Calculator splits calories between wet and dry food.
- If your cat's weight or appetite changes without a clear reason, speak to your vet before changing the diet.
Frequently asked questions
How many calories does a cat need a day?
A neutered adult cat needs about 1.2 × its resting energy requirement (RER = 70 × weight in kg^0.75). A 4 kg cat needs about 238 kcal a day.
What is RER?
Resting Energy Requirement: the calories a healthy cat needs at rest in a comfortable environment, calculated as 70 × body weight in kg raised to the power 0.75.
Why is the factor lower for inactive cats?
Inactive or obesity-prone cats burn less, so vets use a factor of 1.0 × RER instead of 1.2 for a typical neutered adult.
Can I use this calculator for kittens?
No. Kittens need more energy per kilogram to grow, so use the Kitten Food Calculator. Pregnant and nursing cats also need a vet's plan.
How do I use it for a weight-loss plan?
Choose the weight-loss life stage and enter your cat's ideal weight. The calculator uses 0.8 × RER of that weight. Cats must lose weight slowly, so follow your vet's plan.
How do I turn the calories into grams?
Enter the food's kcal per kilogram from the bag and the calculator shows grams a day. Divide the calories by kcal per kilogram and multiply by 1,000 to do it by hand.
Sources
- NRC (2006) Nutrient Requirements of Dogs and Cats, National Academies Press
- Merck Veterinary Manual — Nutritional Requirements of Small Animals (incl. maintenance energy table)
- WSAVA Global Nutrition Guidelines (incl. 9-point BCS charts)
Guides about this
- How Long Are Cats Pregnant? Timeline and Due Date GuideCat pregnancy lasts about 63 to 65 days. See the timeline, how to count from the mating date, what is normal and when to call the vet.
- Cat Years to Human Years: Age Chart (Kitten to 20)A clear cat age chart from kitten to 20 years, how the AAFP/AAHA scale works, the cat life stages and how long cats usually live.
Related calculators
- Cat Food CalculatorWork out your cat's daily calories and how to split them between wet and dry food.
- Cat Treat Calorie CalculatorCheck how many treats your cat can have a day without unbalancing its diet: the 10% rule.
- Kitten Food CalculatorFind out how many calories a growing kitten needs and how much food that is.
- Cat Age CalculatorConvert your cat's age into human years and see its life stage.
Estimates only. Every pet is different — confirm with your veterinarian.