Cat Calorie Calculator

Find how many calories your cat needs each day from its body weight and life stage using the veterinary RER and MER formulas.

Quick Facts

Method
RER = 70 x (weight in kg)^0.75, then MER = RER x life-stage factor
Standard veterinary energy equations (WSAVA / AAHA). 1 kg = 2.20462 lb.

Your Results

Calculated
Daily calories (MER)
-
Feed to this figure to hold weight
Resting energy (RER)
-
Baseline at complete rest
Life-stage factor
-
Multiplier applied to RER

Ready

Enter your cat's weight and life stage, then calculate.

How many calories does a cat need?

This calculator estimates your cat's daily calorie requirement in kilocalories (kcal) using the same two-step method veterinarians use. First it computes the Resting Energy Requirement (RER) — the energy a cat burns at complete rest in a thermoneutral environment. Then it multiplies RER by a life-stage or activity factor to give the Maintenance Energy Requirement (MER), the number you actually feed to.

The formula

The RER uses metabolic body weight, which scales as weight to the three-quarter power rather than linearly:

RER (kcal/day) = 70 × (body weight in kg)0.75

MER (kcal/day) = RER × life-stage factor

A simpler linear approximation, RER ≈ 30 × kg + 70, is sometimes taught for cats between roughly 2 and 45 kg, but this calculator uses the exact exponential form, which is accurate across the full weight range. Because energy scales with kg0.75, a cat that weighs twice as much does not need twice the calories — it needs about 68% more.

Why the life-stage factor matters

RER alone describes a cat doing nothing. Real cats groom, play, digest food, and regulate temperature, so their maintenance needs are higher. Common factors published by the WSAVA and AAHA nutrition guidelines are:

  • Neutered adult: RER × 1.0 to 1.2 (most indoor spayed/neutered cats sit near 1.0)
  • Intact adult: RER × 1.2 to 1.4
  • Weight loss: RER × 0.8 (of ideal, not current, weight)
  • Active or underweight/weight gain: RER × 1.2 to 1.4
  • Kitten (weaning to 4 months): RER × 2.0 to 3.0
  • Kitten (4 months to adult) or lactating queen: RER × 2.5, and lactation can reach RER × 2 to 6 depending on litter size

Reference points

For quick sanity checks, a typical neutered indoor adult cat of ideal weight needs roughly:

  • 3 kg (6.6 lb): RER ≈ 160 kcal/day
  • 4 kg (8.8 lb): RER ≈ 198 kcal/day
  • 4.5 kg (10 lb): RER ≈ 217 kcal/day
  • 5 kg (11 lb): RER ≈ 234 kcal/day
  • 6 kg (13.2 lb): RER ≈ 268 kcal/day

These are RER values; multiply by the life-stage factor for the amount to feed. A 4.5 kg neutered adult at RER × 1.0 needs about 217 kcal/day — often two-thirds to three-quarters of a standard 5.5 oz can of wet food plus a small amount of dry, though exact portions depend on the food's caloric density (printed as kcal/kg or kcal per cup/can on the label).

Frequently Asked Questions

Should I feed the RER or the MER number?
Feed to the MER (maintenance) number for a cat holding a healthy weight. RER is only what the cat burns at complete rest and will underfeed most active cats. Use a below-maintenance factor (about RER × 0.8 of ideal weight) only under veterinary guidance when the cat needs to lose weight.
Should I use my cat's current weight or ideal weight?
For a cat at a healthy body condition, use current weight. For an overweight cat on a diet, base the calculation on estimated ideal weight (or use current weight with the 0.8 weight-loss factor) so you do not simply maintain the excess weight. Your vet can assign a body-condition score to estimate ideal weight.
How do I turn kcal into an actual amount of food?
Divide the daily kcal target by the food's caloric density. Pet food labels list metabolizable energy as kcal/kg and usually kcal per cup or per can. For example, 217 kcal/day ÷ a food providing 4,000 kcal/kg equals about 54 grams of dry food per day. Split it across meals and weigh portions with a kitchen scale for accuracy.
How accurate is this estimate?
The RER/MER equations are population averages. Individual needs vary with genetics, indoor vs. outdoor activity, thyroid and metabolic health, and ambient temperature, so a given cat can differ from the estimate by 20% or more. Treat the number as a starting point, then adjust based on monthly weigh-ins and body-condition scoring. Kittens, pregnant or nursing queens, and cats with medical conditions should be managed with a veterinarian.

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