Cat Food Portion Calculator
Feeding a cat the right amount starts with estimating its daily energy need, which follows a two-step calculation used in feline nutrition. This tool first finds the resting energy requirement, or RER, which is 70 multiplied by the cat's body weight in kilograms raised to the power 0.75, the exponent that captures how energy use scales with body size. It then multiplies the RER by an activity factor that reflects the cat's lifestyle and life stage, returning the estimated daily energy requirement in kilocalories. You convert that into a portion by reading the calorie content on the food label and dividing, then split the total across the day's meals. Enter your own weight and activity factor to set a starting amount for a new food, sanity-check a portion, or plan a careful weight reduction for an overweight indoor cat with a lower factor. Indoor cats commonly carry excess weight, so the activity factor and a watchful eye on body condition matter. Treat the number as a starting estimate, monitor your cat, and confirm with your veterinarian. Every figure here is computed deterministically from the standard RER formula, shown in full below, with a worked example that reconciles exactly to the calculator so you can follow each step.
Daily calories equal the resting energy requirement times an activity factor: kcal = (70 x kg^0.75) x factor. A 4.5 kg cat at an activity factor of 1.2 has an RER of 216.28 kcal and a daily need of about 259.53 kcal.
Daily calorie formula
RER = 70 x (weight in kg)^0.75
Daily energy = RER x activity factor
weight = body weight (kg)
factor = activity / life-stage multiplier
Daily energy = estimated daily need (kcal)
The resting energy requirement is the calories a cat burns at rest; multiplying by the activity factor scales it to a typical day.
Worked example
A 4.5 kg indoor adult cat with an activity factor of 1.2.
- 4.5^0.75 = 3.0897
- RER = 70 x 3.0897 = 216.28 kcal
- Daily energy = 216.28 x 1.2 = 259.53 kcal
The cat needs about 259.53 kcal a day. These are the calculator's default inputs, so the result above matches the widget exactly.
Resting energy requirement by weight
RER rises with body weight, but less than in direct proportion.
| Weight (kg) | RER (kcal) | At factor 1.2 (kcal) |
|---|---|---|
| 3.0 | 159.59 | 191.51 |
| 4.5 | 216.28 | 259.53 |
| 6.0 | 268.32 | 321.99 |
| 7.5 | 316.81 | 380.17 |
Pet food labelling and nutrition oversight: US Food and Drug Administration (FDA).
Cat food portion calculator: frequently asked questions
How are a cat's daily calories estimated?
Start with the resting energy requirement (RER), which is 70 multiplied by the cat's body weight in kilograms raised to the power 0.75. Then multiply the RER by an activity (or life-stage) factor. The result is the estimated daily energy requirement in kilocalories.
What activity factor suits a cat?
Indoor neutered adult cats are often estimated at about 1.2, active cats a little higher, kittens and pregnant or nursing cats much higher. This calculator defaults to 1.2. Pick the factor that matches your cat and confirm with your veterinarian.
How do I convert calories into food?
Find the calorie content on the food label (kcal per cup for dry food, kcal per can or per gram for wet), then divide the daily target by that figure to get the portion. Split it across meals; many cats do well with several small feeds a day.
Is this veterinary advice?
No. It is a starting estimate. A cat's true needs depend on age, health, body condition and metabolism, and obesity is common in indoor cats. Monitor body condition and weight and ask your veterinarian for tailored guidance.
Why the 0.75 exponent?
Energy use scales with body mass to a power close to 0.75 across species, not in direct proportion. Using that exponent gives a more accurate resting-energy estimate than multiplying simply by weight, especially across the range from kittens to large cats.
Official sources
- Pet food labelling, safety and nutrition oversight: US Food and Drug Administration (FDA). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not veterinary, financial, tax, legal or investment advice.