Cat Food Calculator
Calculate how much to feed your cat. Get daily calories and food grams per day from your cat's weight, life stage and the food's kcal per gram.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
These figures are estimates. Always confirm your cat's diet and portions with your veterinarian.
How the Cat Food Calculator Works
This calculator estimates how much to feed your cat each day in both calories and grams of food. Enter your cat’s weight in kilograms, pick a life-stage or goal factor, and enter the food’s energy density in kcal per gram (from the label). It then returns the resting energy requirement, the full daily calorie target, and the matching food portion.
The math follows the standard veterinary approach used by clinics worldwide: calculate the baseline calories a cat burns at rest, scale it for activity and life stage, then translate calories into a real-world portion based on the specific food you feed.
The Formula
RER (kcal) = 70 × (body weight in kg)^0.75 Daily calories = RER × life-stage factor Food (g/day) = daily calories ÷ food kcal per gram
Typical life-stage factors are 1.2 for a neutered adult, 1.4 for an active or intact adult, 0.8 for safe weight loss, and 2.5 for a growing kitten.
Worked Example
For a 4.5 kg neutered adult cat fed a dry food with 3.7 kcal per gram:
- RER = 70 × 4.5^0.75 = 70 × 3.09 = ≈ 216 kcal
- Daily calories = 216 × 1.2 = ≈ 260 kcal/day
- Food = 260 ÷ 3.7 = ≈ 70 grams/day
So this cat needs roughly 260 calories, met by about 70 grams of that dry food per day, ideally split across two or more meals.
Choosing the Right Factor
| Life stage / goal | Factor (× RER) | Notes |
|---|---|---|
| Weight loss | 0.8 | Feed to target weight, reduce gradually, monitor monthly |
| Neutered adult | 1.2 | The default for most spayed/neutered house cats |
| Active / intact adult | 1.4 | Higher activity or not neutered |
| Kitten / growth | 2.5 | Rapid growth; feed several small meals |
Reading Your Food’s Energy Density
The kcal-per-gram figure is the key to an accurate portion. Pet food labels usually state metabolizable energy as kcal per kilogram, per 100 g, or per cup. Convert as needed: dry foods are commonly 3.5-4.2 kcal per gram, while wet/canned foods are far lower — often 0.8-1.2 kcal per gram because of their high water content. Using wet food means a much larger gram weight for the same calories, which is why entering the correct density matters.
Re-check the portion whenever you switch foods, and weigh meals with a kitchen scale rather than guessing with a cup. These numbers are estimates — body condition, age, and health all shift the target, so always confirm your cat’s calorie target and portions with your veterinarian.
Frequently asked questions
How many calories does my cat need per day?+
First find Resting Energy Requirement: RER = 70 × (body weight in kg)^0.75. Then multiply by a life-stage factor — about 1.2 for a neutered adult, 1.4 for an active cat, 0.8 for weight loss, or 2.5 for a growing kitten. A 4.5 kg neutered adult needs roughly 260 kcal a day.
How do I convert daily calories into grams of food?+
Divide the daily calorie target by the food's energy density in kcal per gram, printed on the label as kcal per 100 g or per cup. If your cat needs 260 kcal and the dry food has 3.7 kcal per gram, that is 260 ÷ 3.7 ≈ 70 grams per day.
What is RER for a cat?+
RER, or Resting Energy Requirement, is the calories a cat burns at rest in a thermoneutral environment. It is calculated as 70 × (weight in kg)^0.75. RER is the baseline that gets multiplied by an activity or life-stage factor to give the cat's full daily energy needs.
How much should I feed my kitten compared with an adult cat?+
Kittens use a much higher factor — around 2.5 × RER — because they are growing fast and very active. The same RER formula applies, but the larger multiplier means a kitten eats far more calories per kilogram of body weight than a sedentary adult. Split this into several small meals a day.
Is this cat food calculator a substitute for a vet?+
No. These are general estimates based on standard veterinary energy formulas. Individual needs vary with breed, age, neuter status, health conditions and metabolism. Always confirm your cat's ideal weight, calorie target and portion size with your veterinarian, especially during weight loss or illness.