Cat Calorie Calculator
Enter your cat's weight and life stage to find the Resting Energy Requirement (RER) and the Maintenance Energy Requirement (MER) that veterinary nutritionists use to set daily feeding targets. You also get wet food and dry kibble portion estimates so you can translate kcal directly into a bowl size. Switch between metric and imperial, and tick the treat box to reserve 10% of the daily budget for snacks.
Formula
Worked example
A 4.5 kg neutered adult cat: RER = 70 x 4.5^0.75 = 70 x 3.083 = 215.8 kcal/day. MER = 215.8 x 1.2 = 259 kcal/day. Divided across 2 meals that is about 130 kcal per meal, or roughly 0.68 cups of dry kibble per day.
How the RER and MER formulas work
The Resting Energy Requirement (RER) is the number of calories a cat needs just to stay alive at complete rest - breathing, keeping warm, and running its organs. It is calculated with the formula RER = 70 x bodyweight(kg)^0.75. The exponent 0.75 is the allometric scaling factor: larger animals burn fewer calories per kilogram than smaller ones, so raising weight to 0.75 rather than 1.0 corrects for this effect. The Maintenance Energy Requirement (MER) multiplies RER by a life-stage factor that accounts for growth, reproduction, activity, and whether the cat is spayed or neutered. These formulas are endorsed by the American Animal Hospital Association (AAHA) and the World Small Animal Veterinary Association (WSAVA).
Choosing the right life-stage category
Kittens under four months old need roughly three times their resting requirement because they are doubling in size rapidly. From four months to one year, that factor drops to 2.0 as growth slows. Most neutered adult indoor cats sit at 1.2x RER, while intact adults need a little more at 1.4x. Active or outdoor cats that hunt, climb, and run have the highest adult need at 1.6x. Pregnant queens start at 2.0x in late gestation, and lactating mothers need as much as 2.5x because producing milk is energetically expensive. Senior cats (generally 11 years and older) often move less and may need closer to 1.1x, though some seniors actually need more calories if they lose muscle mass - your vet can help interpret body condition. If your cat is overweight, the weight-loss preset uses 0.8x RER, but calorie restriction in cats should always be gradual and monitored by a veterinarian to avoid hepatic lipidosis.
Translating calories into bowl sizes
This calculator estimates portion size using two average densities: 380 kcal per cup for dry kibble and 200 kcal per standard 5.5-ounce wet can. These are midpoints - actual values vary widely by brand and formula. The safest approach is to read the caloric density from your specific product label (expressed as kcal/kg or kcal/cup) and divide your cat's MER by that number. Wet food can also be measured in grams if the label gives kcal/100g. For a mixed diet, use the calculator's per-meal budget and allocate a fraction to each food type proportionally.
The 10% treat rule and why it matters
Treats are often calorie-dense and nutrient-imbalanced compared with complete cat foods. Veterinary nutritionists recommend keeping treats to no more than 10% of total daily calories. If you tick the treat reserve box, the calculator subtracts that 10% from the daily budget and divides only the remaining 90% by the number of meals. This keeps total intake constant while giving you a guilt-free treat allowance. For a cat needing 260 kcal/day, that is 26 kcal for treats - roughly 3-4 small commercial treats - and 117 kcal per meal across two feedings.
Life-stage multipliers (AAHA 2021)
| Life stage | Multiplier | Notes |
|---|---|---|
| Kitten (0-4 months) | 3.0x RER | Rapid growth phase |
| Kitten (4-12 months) | 2.0x RER | Continued growth |
| Neutered/Spayed adult | 1.2x RER | Most indoor cats |
| Intact adult | 1.4x RER | Slightly higher need |
| Active/outdoor adult | 1.6x RER | High activity |
| Pregnant | 2.0x RER | Late gestation |
| Lactating | 2.5x RER | Nursing kittens |
| Senior (11+ yrs) | 1.1x RER | Reduced activity |
| Weight loss | 0.8x RER | Vet-supervised only |
Factors applied to RER to estimate MER. Source: 2021 AAHA Nutrition and Weight Management Guidelines.
Frequently asked questions
How many calories does a typical house cat need per day?
Most neutered adult indoor cats need between 180 and 300 kcal/day, depending on body weight. A 4 kg neutered cat needs about 235 kcal/day; a 6 kg cat about 320 kcal/day. Intact adults, kittens, and very active cats need more, while overweight cats on a weight-loss plan may be restricted to less.
What is RER and how is it different from MER?
RER (Resting Energy Requirement) is the baseline calories a cat burns just sustaining life at complete rest - no movement, no digestion. MER (Maintenance Energy Requirement) is RER multiplied by a life-stage factor that accounts for activity, growth, and reproductive status. MER is the daily target you actually feed to.
My cat is overweight. How do I use this calculator to help?
Select the "Weight loss" life stage (0.8x RER). Enter your cat's current weight to get the restricted calorie target. Never reduce calories by more than about 20-25% of normal maintenance at once, and always consult your vet first - sudden calorie restriction can trigger hepatic lipidosis (fatty liver disease) in cats, which is potentially fatal.
How much wet food should I feed my cat per day?
Divide your cat's MER by the caloric density on your wet food's label. If the label says 200 kcal per 5.5-oz can and your cat needs 260 kcal/day, that is 1.3 cans per day. The estimate in this calculator uses 200 kcal/can as an average, but densities can range from about 150 to 250 kcal per standard can.
Do senior cats need fewer calories?
It depends. Many cats over 11 years old move less and can gain weight on the same food they ate as middle-aged adults, so a modest reduction (the 1.1x senior preset) is often appropriate. However, some seniors lose muscle mass and need higher protein and even more total calories to maintain body condition. Body condition scoring every few months is the most reliable guide.
Does the formula work for kittens?
Yes. Kittens under four months use a 3.0x RER multiplier, reflecting their intense growth phase. From four months to one year the multiplier is 2.0x. Young kittens may also need free-choice feeding rather than fixed portion sizes - check with your vet.
Is this calculator accurate enough to replace advice from a vet?
The RER/MER formulas are the standard veterinary starting point, but they predict average needs. Individual cats vary significantly based on genetics, health conditions, coat length, and environment. Use this as a first estimate, then adjust over 2-4 weeks based on how your cat's body condition changes. Any cat with a health condition, or one on a weight-loss or weight-gain plan, should be monitored by a veterinarian.