Pet Calorie Requirement Calculator
Every feeding plan for a cat or dog begins with one number: the resting energy requirement, or RER, the calories the animal burns at complete rest before any activity is added. This calculator computes the RER from the standard formula, 70 multiplied by the pet's body weight in kilograms raised to the power 0.75, the exponent that describes how energy use scales with body size across mammals. The RER is the foundation; to reach a full daily target you multiply it by an activity or life-stage factor, typically from about 1.2 for an inactive pet up to 1.6 or more for active adults and higher again for growth. Keeping the resting baseline separate makes it easy to apply the right factor and to adjust as the life stage changes. Enter your pet's weight to get the RER for a cat or a dog, then layer your chosen factor on top, or sanity-check a portion against the food label. The 0.75 exponent is what makes the estimate hold from tiny pets to large ones, where a per-kilogram rule would fail. 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.
The resting energy requirement is 70 times body weight in kilograms raised to the power 0.75: RER = 70 x kg^0.75. A 10 kg pet has a resting energy requirement of 393.64 kcal per day before any activity factor.
Resting energy requirement formula
RER = 70 x (weight in kg)^0.75
weight = body weight (kg)
RER = resting energy requirement (kcal per day)
Daily need = RER x activity factor
The resting energy requirement is the baseline; multiply by an activity or life-stage factor to get the full daily energy need.
Worked example
A pet weighing 10 kg.
- 10^0.75 = 5.6234
- Multiply by 70: 70 x 5.6234 = 393.64
- Resting energy requirement = 393.64 kcal
The RER is 393.64 kcal a day. These are the calculator's default inputs, so the result above matches the widget exactly.
Resting energy requirement by weight
RER climbs with weight, but more slowly than weight itself.
| Weight (kg) | RER (kcal) |
|---|---|
| 5 | 234.06 |
| 10 | 393.64 |
| 20 | 662.02 |
| 40 | 1,113.34 |
Pet food labelling and nutrition oversight: US Food and Drug Administration (FDA).
Pet calorie requirement calculator: frequently asked questions
What is the resting energy requirement?
The resting energy requirement, or RER, is the calories a pet uses at complete rest in a thermoneutral environment, before any activity. It is the baseline that all daily feeding estimates build on. The formula is 70 multiplied by the body weight in kilograms raised to the power 0.75.
How do I find the full daily need?
Multiply the RER by an activity or life-stage factor. Typical factors range from about 1.2 for an inactive or weight-loss pet up to 1.6 or more for active adults, with higher values for growth, pregnancy and lactation. The RER on its own is the resting baseline only.
Does this work for both cats and dogs?
Yes. The RER formula is the same across cats and dogs and many other mammals, because it rests on how energy use scales with body mass. The difference between species and individuals comes through the activity factor you apply on top of the RER.
Why raise weight to the power 0.75?
Metabolic rate scales with body mass to roughly the three-quarter power, an empirical relationship that holds across a wide range of species. Using 0.75 rather than 1.0 prevents the large overestimate for big animals and underestimate for small ones that a simple per-kilogram rule produces.
Is this a replacement for veterinary advice?
No. The RER is a starting estimate. Real needs vary with health, body condition, age and metabolism. Use the number as a baseline, watch your pet's body condition, and ask your veterinarian for individual feeding guidance.
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.