Cat RER Calculator (Resting Energy Requirement)
A cat's resting energy requirement is determined using the universal veterinary exponential formula:
RER = 70 × (body weight in kg)0.75
This indicates the baseline calories your cat burns each day at rest. Multiply this figure by a feline life-stage multiplier (MER)—such as 1.2–1.4× for neutered adults or 1.0× for sedentary indoor cats—to determine precise daily feeding portions.
Cat RER & Daily Calorie Calculator
Enter your cat's weight to calculate the exact Resting Energy Requirement (RER) and customized daily feeding ranges based on life stage.
Clinical Disclaimer: Caloric estimates provide a scientific starting baseline for healthy pets. Individual metabolism varies by up to 20%. For pets with medical conditions, diabetes, renal disease, or active weight management goals, always follow your veterinarian's tailored prescription plan.
Weight Loss Note: If your cat is overweight, calculate calories using their target (ideal) weight, not their current weight.
Resting Energy Requirement (energy burned at rest in a thermoneutral environment)
Estimated Daily Food Intake by Life Stage (MER)
Maintenance Energy Requirement (MER) = RER × Life Stage Factor (AAHA 2021 guidelines)
Standard healthy indoor spayed/neutered cat
Unneutered adult cat
Sedentary indoor cats with low energy expenditure
Vet-supervised caloric reduction using target body weight
Rapidly growing kittens up to 1 year of age
Pregnant queen throughout pregnancy
Nursing queen depending on litter size
High activity or outdoor exploration
Working or farm cats with extensive daily physical activity
The Cat RER Formula, Step by Step
While dogs and cats share the same fundamental RER biological formula (70 × kg0.75), cats differ significantly in their metabolic multipliers, strict obligate carnivore protein demands, and vulnerability during calorie reduction.
Worked Example: 10 lb Cat
- Convert weight to kilograms: 10 lb ÷ 2.20462 = 4.5 kg (or 10 × 0.453592).
- Calculate metabolic body weight: (4.5)0.75 ≈ 3.11.
- Calculate RER: 70 × 3.11 ≈ 218 kcal/day.
- Apply feline life stage factor: A healthy neutered adult cat at 1.2–1.4 × RER requires approximately 261–305 kcal/day. An inactive indoor cat at 1.0 × RER requires approximately 218 kcal/day.
Cat RER Lookup Table by Pounds (4–20 lb)
Exact calculations generated directly from code: RER = 70 × (kg)0.75. Includes neutered adult (1.2–1.4×), inactive indoor (1.0×), and target weight-loss (0.8×) columns.
| Weight (lb) | Weight (kg) | RER (kcal) | Neutered (1.2–1.4×) | Inactive (1.0×) | Weight Loss (0.8×)* |
|---|---|---|---|---|---|
| 4 lb | 1.8 kg | 109 | 131–153 | 109 | 88 |
| 5 lb | 2.3 kg | 129 | 155–181 | 129 | 103 |
| 6 lb | 2.7 kg | 148 | 178–208 | 148 | 119 |
| 7 lb | 3.2 kg | 167 | 200–233 | 167 | 133 |
| 8 lb | 3.6 kg | 184 | 221–258 | 184 | 147 |
| 9 lb | 4.1 kg | 201 | 241–281 | 201 | 161 |
| 10 lb | 4.5 kg | 218 | 261–305 | 218 | 174 |
| 11 lb | 5.0 kg | 234 | 280–327 | 234 | 187 |
| 12 lb | 5.4 kg | 249 | 299–349 | 249 | 200 |
| 13 lb | 5.9 kg | 265 | 318–371 | 265 | 212 |
| 14 lb | 6.4 kg | 280 | 336–392 | 280 | 224 |
| 15 lb | 6.8 kg | 295 | 354–413 | 295 | 236 |
| 16 lb | 7.3 kg | 310 | 371–433 | 310 | 248 |
| 18 lb | 8.2 kg | 338 | 406–473 | 338 | 270 |
| 20 lb | 9.1 kg | 366 | 439–512 | 366 | 293 |
* For weight loss, select the row corresponding to your cat's target ideal weight, not current weight. All values in kcal/day.
Cat RER Lookup Table by Kilograms (1.5–10 kg)
Standard metric reference table for feline veterinary medicine.
| Weight (kg) | Weight (lb) | RER (kcal) | Neutered (1.2–1.4×) | Inactive (1.0×) | Weight Loss (0.8×) |
|---|---|---|---|---|---|
| 1.5 kg | 3.3 lb | 95 | 114–133 | 95 | 76 |
| 2 kg | 4.4 lb | 118 | 141–165 | 118 | 94 |
| 2.5 kg | 5.5 lb | 139 | 167–195 | 139 | 111 |
| 3 kg | 6.6 lb | 160 | 191–223 | 160 | 128 |
| 3.5 kg | 7.7 lb | 179 | 215–251 | 179 | 143 |
| 4 kg | 8.8 lb | 198 | 238–277 | 198 | 158 |
| 4.5 kg | 9.9 lb | 216 | 260–303 | 216 | 173 |
| 5 kg | 11.0 lb | 234 | 281–328 | 234 | 187 |
| 6 kg | 13.2 lb | 268 | 322–376 | 268 | 215 |
| 7 kg | 15.4 lb | 301 | 361–422 | 301 | 241 |
| 8 kg | 17.6 lb | 333 | 400–466 | 333 | 266 |
| 9 kg | 19.8 lb | 364 | 436–509 | 364 | 291 |
| 10 kg | 22.0 lb | 394 | 472–551 | 394 | 315 |
The Linear Formula (30 × kg + 70) for Cats
In feline medicine, the linear shortcut (30 × kg + 70) aligns relatively closely for normal adult cats between 2.5 and 5 kg (for example, at 4.5 kg, the exponential formula yields 218 kcal vs 205 kcal with the linear formula). However, veterinary nutritionists recommend the exponential formula (70 × kg0.75) as the gold standard across all body sizes.
MER Multipliers for Cats (AAHA 2021 Guidelines)
Maintenance Energy Requirement factors accounting for neuter status and activity in felines.
| Life Stage | Multiplier (× RER) | Clinical Guidance |
|---|---|---|
| Neutered adult | 1.2–1.4 | Standard healthy indoor spayed/neutered cat |
| Intact adult | 1.4–1.6 | Unneutered adult cat |
| Inactive or obesity-prone | 1.0 | Sedentary indoor cats with low energy expenditure |
| Weight loss (target weight) | 0.8 | Vet-supervised caloric reduction using target body weight |
| Growth (kittens) | 2.5 | Rapidly growing kittens up to 1 year of age |
| Gestation | 1.6–2.0 | Pregnant queen throughout pregnancy |
| Lactation | 2.0–6.0 | Nursing queen depending on litter size |
| Light work | 1.6–2.0 | High activity or outdoor exploration |
| Moderate work | 2.0–5.0 | Working or farm cats with extensive daily physical activity |
Cats must never undergo rapid weight loss or severe calorie restriction. When an overweight cat is starved or deprived of sufficient daily calories, their liver is flooded with non-esterified fatty acids, precipitating hepatic lipidosis, an acute and potentially fatal liver failure.
- Safe weight loss rate: 0.5% to 1.0% of body weight per week (e.g. 0.05–0.1 lb per week for a 10 lb cat).
- Never feed below 70% of resting energy requirements without direct, continuous veterinary supervision.
- If a cat stops eating for more than 24–48 hours, seek emergency veterinary care immediately.
Indoor Cat Energy Expenditure:
Indoor companion cats spend an average of 18 hours daily sleeping or resting. Consequently, many healthy neutered adult indoor cats require energy at the lower end of the multiplier range (1.0–1.2 × RER). Evaluate your cat's Body Condition Score (BCS, targeting 5 on the 9-point WSAVA scale) every 2 to 4 weeks and calibrate food portions accordingly.
Frequently Asked Questions
What does RER mean for cats?
RER stands for Resting Energy Requirement. It represents the baseline daily calories (in kcal/day) a cat requires to sustain life at rest in a thermoneutral environment, powering basic involuntary functions such as cellular repair, cardiac output, renal filtration, and breathing.
How many calories does an average indoor cat need per day?
Most healthy adult indoor neutered cats weigh between 8 and 11 lbs (3.6–5.0 kg) and require roughly 180 to 250 kcal/day. Because indoor lifestyles involve low physical activity, many neutered cats maintain ideal weight closer to 1.0–1.2 × RER.
Why do neutered cats require fewer calories?
Neutering or spaying removes sex hormones, which reduces a cat's basal metabolic rate by approximately 20–25%. At the same time, neutered cats often display increased appetite. Adjusting caloric intake down to the neutered multiplier (1.2–1.4 × RER, or 1.0 × RER for sedentary cats) prevents post-neuter obesity.
Which weight do I use for an overweight cat?
Always use your cat's target (ideal) body weight when calculating calories for weight loss. Feeding based on an overweight cat's current weight provides an excess of calories and prevents weight reduction.
Why is rapid weight loss dangerous for cats?
Unlike humans or dogs, cats that undergo severe calorie restriction or anorexia mobilize body fat rapidly to the liver, leading to hepatic lipidosis (fatty liver syndrome). This condition can be fatal without intensive medical intervention. A safe, veterinarian-approved feline weight loss rate is strictly 0.5% to 1.0% of body weight per week.
Is this calculator a medical feeding plan?
No. This calculator provides estimates based on peer-reviewed veterinary formulas from the National Research Council (NRC 2006) and the American Animal Hospital Association (AAHA 2021). For cats with kidney disease (CKD), diabetes mellitus, FLUTD, or hyperthyroidism, consult your veterinarian for an individualized medical nutrition plan.
Related Tools & Feeding Guides
- → Full Pet Calorie Calculator — Personalized daily portions and canned/dry food mixes.
- → Cat Breeds Directory — Calorie needs, weight standards, and activity profiles across breeds.
- → Indoor Cat Feeding Guide — Complete nutrition plan by age, weight & life stage.
- → Cat Calorie Calculator Blog Guide — Veterinary formula breakdown and portion control tips.
- → Dog RER Calculator — Canine resting energy calculations and worked examples.
Scientific Sources & Clinical References:
- American Animal Hospital Association (AAHA). 2021 AAHA Nutrition and Weight Management Guidelines for Dogs and Cats.
- National Research Council (NRC). Nutrient Requirements of Dogs and Cats. National Academies Press, 2006.
- World Small Animal Veterinary Association (WSAVA) Global Nutrition Committee. Nutritional Assessment Guidelines.
- Pet Nutrition Alliance (PNA). Veterinary Energy & Calorie Calculation Reference.
- Merck Veterinary Manual. Daily Maintenance Energy Requirements of Dogs and Cats.