This pet calorie calculator estimates your dog’s or cat’s daily calorie needs from body weight and life-stage factor — the RER × DER method vets use — so feeding amounts stop being guesswork.

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RER = 70 × kg^0.75 — the Metabolic Scaling Law

Resting energy follows Kleiber’s ¾-power law across species (why a 40 kg dog needs ~5.7× a 2 kg cat, not 20×). DER multiplies RER by neutering, activity and goal. Species framing: our Dog Age Calculator handles a pet’s other famous number. Part of our Everyday Life Calculators collection.

Worked Examples (Verified)

  • 10 kg neutered dog (defaults): RER = 70 × 10^0.75 = 394 kcal; DER ×1.6 = 630 kcal/day — on 380 kcal/cup food ≈ 1.66 cups
  • 5 kg indoor neutered cat: RER = 234 kcal; ×1.2 = 281 kcal/day — on 400 kcal/cup ≈ 0.70 cups; the free-feeding bowl erases this arithmetic entirely
  • Weight-loss contrast: the same 10 kg dog at ×1.0 eats 394 kcal — a 37% cut from maintenance, which is why “a little less kibble” so often isn’t
  • Scale sanity: doubling weight (10 → 20 kg) raises RER only ×1.68 (394 → 662) — per-kilo needs fall as animals grow, the ¾ law in action

Feeding Practice

  • Start at the calculator’s figure, then let body condition referee: weigh every 2–4 weeks and nudge ±10%.
  • Convert honestly: food labels state kcal/cup or kcal/kg — wet food is ~¼ the density of kibble; measuring cups lie by ±20% versus a kitchen scale.
  • Treats, chews and “just a bite” of dinner are calories with no exemption; budget them inside DER.
  • Growth, pregnancy, lactation, working dogs and illness blow past the standard factors — those are veterinary conversations, not dropdown settings.

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Frequently Asked Questions

How many calories does my dog need per day?

RER (70 × weight-kg^0.75) × a life-stage factor: a neutered adult dog uses ×1.6 — so a 10 kg dog needs ~630 kcal/day. Intact adults ×1.8, weight loss ×1.0, puppies ×2–3. This calculator applies the standard factors; adjust by body condition over time.

How many calories does a cat need?

Indoor neutered cats run ×1.2 on RER: a 5 kg cat ≈ 281 kcal/day. Cats’ margin is thin — small daily overfeeds compound fast on a 234 kcal resting budget, which is why measured meals beat free-feeding for indoor cats.

Why is the formula weight to the 0.75 power?

Metabolism scales with body mass^0.75 across species (Kleiber’s law) — heat loss and tissue turnover track surface-ish geometry, not raw weight. It’s why calorie needs per kilogram fall as animals get bigger, and why linear “30 kcal per kg” rules overfeed large dogs.

How do I turn calories into cups of food?

Daily kcal ÷ label kcal-per-cup: 630 ÷ 380 ≈ 1.66 cups. Weigh the food instead if weight management matters — scooped cups vary wildly with kibble shape and enthusiasm. Split into 2 meals for dogs, 2+ for cats.

Are treats included in the daily calories?

Yes — they must be. Vets’ rule: treats ≤ 10% of daily calories (63 kcal on the default dog’s budget ≈ a small biscuit or two). Unbudgeted treats are the most common reason “we feed exactly what the bag says” still produces a round pet.

Is this pet calorie calculator free?

Yes — free, instant, no sign-up. An estimate to start the conversation with your vet, not a prescription.