How this calculator works
Resting energy requirement uses body mass to the three-quarter power. Merck gives starting daily factors of 1.2 for neutered adults, 1.4 for intact adults and 2.5 for healthy kittens. Requirements vary with growth stage, activity and disease. Rather than assign a generic restriction or gain plan, those options require a factor chosen with your veterinary team. Reverse weight is an algebraic result, not a target-weight recommendation.
Formula
RER (kcal/day) = 70 × mass (kg)^0.75. Daily energy = RER × factor. Implied mass = [daily kcal/(70 × factor)]^(4/3). Factor = daily energy/RER. A kcal equals 4,184 J.
Worked example
At 1 kg, RER is 70 kcal/day, and the neutered-adult factor gives 84 kcal/day. At 16 kg, the mathematical RER is 560 kcal/day and the intact-adult estimate is 784 kcal/day. The latter example demonstrates the arithmetic, not a typical healthy cat weight.
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Frequently asked questions
Should I use current or ideal weight?
For a routine healthy adult estimate, use the measured weight. A weight-management plan may need a veterinarian-selected target instead.
Do kittens of all ages need exactly 2.5 times RER?
No. It is a broad starting estimate. Growth rate and stage affect intake, so follow an appropriate kitten feeding plan and track the growth curve.
Is a cat not eating a weight-loss opportunity?
No. Loss of appetite can be serious, especially in overweight cats. Contact your veterinarian rather than using this calculator to restrict food.