Veterinary RER formula (WSAVA) — instant result
Cat Food Ration Calculator
How many grams of kibble or wet food should I give my cat each day? The answer depends on weight, age, activity level and reproductive status. This calculator uses the RER (Resting Energy Requirement) formula recommended by veterinary nutritionists (WSAVA 2021) to estimate your cat's caloric needs and convert them into food grams.
Dry kibble
Default: 380 kcal/100g (kibble) or 85 kcal/100g (wet). Check your food label.
Nutritional assessment
4 kg
Body condition score (BCS)
Ideal weight
Ideal
4 kg
Ideal weight
Recommended daily ration
in 2 meals of 32 g each · 238 kcal / day
💡 A moderately active neutered cat should be fed twice daily at fixed times. Avoid snacking and monitor monthly weight changes.
Nutritional profile
Food for neutered cats
Proteins
ModerateFat
LowCarbohydrates
ModerateRecommended water intake
200 ml / day
Estimated monthly food cost
Based on average Canadian market prices. Check your food label for exact caloric density.
Indicative values based on the veterinary RER formula (WSAVA). Consult your veterinarian to adapt the ration to your cat's specific needs.
How does the calculation work?
The RER formula calculates resting energy needs: RER (kcal/day) = 70 × weight(kg)^0.75. This number is multiplied by a factor that accounts for age, neutering status, body condition score, goal and activity level. The food caloric density (kcal/100g) then converts the result to grams.
Frequently asked questions
How many grams of kibble per day for a 4 kg cat?
For a neutered adult cat weighing 4 kg with moderate activity and ideal body condition (BCS 4–5), the recommended daily ration is approximately 55–65 grams of standard dry kibble (380 kcal/100g) based on the veterinary RER formula: RER = 70 × 4^0.75 × 1.2, giving ~214 kcal/day ÷ 3.8 = ~56g.
Does a neutered cat need less food?
Yes. Neutering reduces a cat's energy needs by approximately 15–20%. The MER factor drops from 1.4 (intact moderate adult) to 1.2 (neutered moderate adult). Adjust the ration within 4 weeks of neutering to prevent weight gain.
What is the difference in ration between dry and wet food?
Dry kibble contains approximately 380 kcal per 100 g, versus 85 kcal per 100 g for wet food. A cat therefore needs roughly 4.5 times more wet food by weight than kibble for the same caloric intake. Wet food is high in water (70–80%), which benefits hydration and kidney health.
What is a cat's body condition score (BCS)?
The Body Condition Score (BCS) is a 1–9 scale used by veterinarians to assess body fat. BCS 1–3: too thin (ribs visible). BCS 4–5: ideal (ribs palpable but not visible). BCS 6–7: overweight. BCS 8–9: obese. This score allows precise caloric adjustment that body weight alone cannot reflect.