Cat RER Calculator
Calculate your cat’s Resting Energy Requirement (RER)
Cat Weight
Weight Unit
What Is the Cat RER Formula?
The RER (Resting Energy Requirement) is the scientific baseline for calculating how many calories a cat needs per day. It represents the energy required just to maintain basic bodily functions at rest — breathing, circulation, organ function. The veterinary formula is:
RER = 70 × (body weight in kg)^0.75
This is then multiplied by a life stage factor to give the MER (Maintenance Energy Requirement) — the actual daily calorie target for your cat.
RER vs MER: What’s the Difference?
| Term | Meaning | Use |
|---|---|---|
| RER | Resting Energy Requirement | Baseline; calories at rest |
| MER | Maintenance Energy Requirement | RER x life stage factor = daily feed target |
| DER | Daily Energy Requirement | Same as MER; used interchangeably |
Life Stage Multipliers (RER x Factor = Daily kcal)
- Kitten: RER x 2.5
- Neutered adult: RER x 1.0
- Intact adult: RER x 1.2
- Active / outdoor: RER x 1.4
- Weight loss: RER x 0.8
- Pregnant: RER x 2.0
- Nursing: RER x 2.6
- Senior: RER x 0.9
For a practical feeding plan, use our cat calorie calculator which applies these factors automatically, or our cat food calculator to convert kcal into servings.
Why RER Matters for Feline Health
Using RER as your starting point ensures you’re feeding based on your cat’s physiology, not rough guesses. It’s the same method used by veterinary nutritionists worldwide. Combined with regular weight monitoring using our cat weight calculator, it gives you a complete, science-based nutrition system.
FAQs
What is the RER for a 10 lb cat?
A 10 lb (4.5 kg) cat has an RER of approximately 210 kcal/day. A neutered adult needs around 210 kcal, while a kitten of the same weight would need ~525 kcal.
What is Purina’s MER calculator for cats?
Purina uses the same base formula (70 x BW^0.75) and applies life stage multipliers similar to those above. Their interactive tool on their website applies brand-specific food data alongside the formula.
Is RER the same as BMR in cats?
They are similar but not identical. BMR (Basal Metabolic Rate) is measured under strict fasting conditions. RER accounts for minor activity and is the practical standard used in veterinary nutrition.
Conclusion
The cat RER calculator above gives you the scientific foundation for all feline feeding decisions. Use it alongside our feeding schedule calculator and cat age calculator for a complete, vet-aligned nutrition plan.
Questions about cat RER or nutrition? Leave a comment below!