Cat Resting Energy Requirement (RER) Explained
RER is the starting point for every cat calorie plan. Learn the formula, a worked example and the life stage factors vets use.
What RER means
Resting energy requirement is the energy a cat burns while resting in a comfortable place. It covers breathing, circulation and keeping warm. It is the base number vets use before adding extra for life stage and activity.
The formula
RER = 70 × (weight in kg)0.75. A 10 lb cat weighs 4.5 kg. Its RER is about 218 calories a day. Smaller cats need more energy per pound than bigger cats, which is why the formula uses a power, not a straight multiple.
From RER to daily calories
Multiply RER by a factor.
- Kitten under 4 months: about 2.5
- Kitten 4 to 12 months: about 2.0
- Intact adult: about 1.4
- Neutered adult: about 1.2
- Weight loss: about 0.8 of the ideal-weight RER
Limits of the formula
Every cat is different. Two cats of the same weight can differ by 20 percent. Use the result as a trial amount and let body weight and body condition tell you if it works.
Sources and further reading: WSAVA Global Nutrition Guidelines; AAHA Nutrition and Weight Management Guidelines; NRC Nutrient Requirements of Dogs and Cats. This article is educational and does not replace advice from your veterinarian.