What Is the Cat Food Calculator?
This tool estimates how many grams of food your cat needs each day. It uses the same energy-based method veterinarians use: first it calculates your cat's Resting Energy Requirement (RER), multiplies it by a life-stage activity factor to get the Daily Energy Requirement (DER), then converts those calories into grams using the calorie density printed on your food's label.
How to Use It
Enter your cat's weight in kilograms, choose the life stage or activity level that best matches your cat, and type the food's energy in kilocalories per 100 grams (found on the package as "ME" or "metabolizable energy"). The calculator returns the recommended daily portion in grams plus the underlying RER and DER in calories.
The Formula Explained
The RER is calculated as \(70 \times \text{weight}^{0.75}\), an exponential curve that reflects how smaller animals burn more energy per kilogram. The DER multiplies RER by an activity factor: about 1.2 for a typical neutered indoor adult, up to 2.0–2.5 for kittens or pregnant/lactating cats, and around 1.0 for seniors or weight loss. Finally, daily calories are divided by the food's calories per gram to give grams per day.
$$\text{Food (g/day)} = \frac{70 \cdot \text{Weight}^{0.75} \cdot \text{Activity}}{\text{kcal per 100 g} / 100}$$
Worked Example
A 4 kg neutered indoor cat eating dry food rated 350 kcal/100 g:
$$\text{RER} = 70 \times 4^{0.75} = 70 \times 2.828 \approx 198 \text{ kcal}$$$$\text{DER} = 198 \times 1.2 \approx 238 \text{ kcal}$$$$\text{Food energy} = 350/100 = 3.5 \text{ kcal/g}$$$$\text{Daily food} = 238 \div 3.5 \approx \textbf{68 grams per day}$$FAQ
Is this a substitute for veterinary advice? No. It is an estimate; always confirm portions with your vet, especially for weight management or medical diets.
Where do I find kcal per 100 g? Check the food label for "metabolizable energy." Wet food is usually 70–100 kcal/100 g; dry food is often 300–400 kcal/100 g.
Should I split into multiple meals? Yes — divide the daily grams across 2–4 feedings, and adjust gradually based on your cat's body condition.
