# Your pet's daily calories, from RER and MER

> How many calories does your pet actually need each day? Enter body weight, species, and life stage to get a maintenance energy range (MER) in kcal/day, built from the resting energy requirement (RER = 70 × BW^0.75) of the WSAVA / NRC 2006 formula. Results are educational guidance, not a feeding prescription.

## Who stands behind this calculator

Written by [Patrick Li](/authors/patrick-li/). Editorially reviewed 2026-09-01 · Evidence checked 2026-09-01.

Evidence: Multiple sources agree · Evidence from a closely related context.

No veterinarian has reviewed this page. It is educational guidance checked by the author against the cited sources — for health decisions, talk to your vet.

PetGuideCalc reserves its highest trust label for pages that a named veterinary professional has reviewed. This page does not carry that label.

The estimate is an educational starting point for healthy pets. It does not diagnose conditions or replace an individualized feeding plan — a pet that is losing weight, gaining weight unexpectedly, or managing illness needs a target set with a veterinarian.

## Direct answer

RER (resting energy requirement) is the calories a healthy animal burns at rest in a thermoneutral environment. The standard formula is RER = 70 × BW^0.75 kcal/day, where BW is body weight in kilograms. MER (maintenance energy) multiplies RER by a life-stage factor to estimate a pet's daily caloric need. For a 10 kg adult neutered dog, RER is about 394 kcal/day and MER is the 472–551 kcal/day range from the 1.2–1.4 factor.

## Calculator

Use the interactive calculator on the page: https://petguidecalc.com/tools/rer-calculator/ — pick a species and life stage, enter body weight in kg or lb, and get RER (single value) plus a MER range (kcal/day) from the WSAVA / NRC 2006 factor bands.

## Species supported

The RER formula is the same across species; only the typical adult weight range differs.

| Species | Typical adult weight (kg) | Typical adult weight (lb) | Note |
|---|---|---|---|
| Dog | 4–50 | 8.8–110.2 | Same 70 × BW^0.75 formula; use life-stage factor for MER. |
| Cat | 3–7 | 6.6–15.4 | Same 70 × BW^0.75 formula; use life-stage factor for MER. |
| Hamster | 0.03–0.2 | 0.1–0.4 | Same 70 × BW^0.75 formula; use life-stage factor for MER. |
| Rabbit | 1–8 | 2.2–17.6 | Same 70 × BW^0.75 formula; use life-stage factor for MER. |
| Hedgehog | 0.25–0.6 | 0.6–1.3 | Same 70 × BW^0.75 formula; use life-stage factor for MER. |

## MER factor bands by life stage

Factor × RER = MER (kcal/day). Peak-lactation is wide because small pets and large litters trend toward the high end.

| Life stage | MER factor | Source | Note |
|---|---|---|---|
| Adult, neutered | 1.2–1.4× RER | NRC 2006 — Nutrient Requirements of Dogs and Cats | Typical maintenance for spayed / neutered adult dogs and cats. |
| Adult, intact | 1.4–1.6× RER | NRC 2006 — Nutrient Requirements of Dogs and Cats | Higher maintenance for unspayed / unneutered adults. |
| Adult, working / active | 1.6–1.8× RER | NRC 2006 — Nutrient Requirements of Dogs and Cats | Working dogs, agility, or highly active pets. |
| Growing puppy / kitten | 2–3× RER | NRC 2006 — Nutrient Requirements of Dogs and Cats | Weaning through growth; needs peak calories for development. |
| Late gestation | 1.5–2× RER | WSAVA Global Nutrition Assessment Guidelines | Final third of gestation; supports fetal growth. |
| Peak lactation | 4–8× RER | WSAVA Global Nutrition Assessment Guidelines | Peak milk production; large litters and small pets trend toward the high end. |

## How the energy estimate is calculated

Resting energy requirement uses the WSAVA / NRC 2006 formula RER = 70 × BW^0.75 kcal/day, where BW is body weight in kilograms. For a 10 kg adult dog, RER ≈ 394 kcal/day. The 0.75 exponent reflects metabolic scaling: a 10 kg dog does not need 10× the calories of a 1 kg dog — closer to 5.6×.

Maintenance energy multiplies RER by a life-stage factor. WSAVA lists 1.2–1.4 for adult neutered pets, 1.4–1.6 for adult intact pets, 1.6–1.8 for working / highly active pets, 2–3 for growth, 1.5–2 for late gestation, and 4–8 for peak lactation. A 10 kg neutered adult dog lands at 472–551 kcal/day.

Body composition matters as much as the math: an overweight pet should be fed to its ideal weight, not its current weight, to avoid reinforcing obesity. Use the result as a starting point and adjust based on body condition score (BCS) — adjust food every 1–2 weeks until the BCS hits the 4–5 / 9 target.

Small mammals scale dramatically. A 0.05 kg adult-active hamster needs only about 7.4 kcal/day RER (11.8–13.3 kcal/day MER), while a 4 kg lactating queen's MER jumps to 792–1584 kcal/day — peak lactation is the highest-demand life stage in the table.

## Calorie questions, answered

**Q: How accurate is the 70 × BW^0.75 RER formula for cats and dogs?**

It is the standard formula in WSAVA Global Nutrition Guidelines and NRC 2006 for healthy adult animals at rest, and works well for dogs and cats in the typical 2–50 kg range. For very small pets (under 2 kg) and morbidly obese animals, the estimate drifts — use ideal body weight, not current weight, when BCS is above 6/9.

**Q: Should I feed my pet the MER value or the RER value?**

Feed to MER for healthy adults. RER is the energy used lying still — it underestimates maintenance by 20–80% depending on life stage, so feeding to RER typically causes weight loss. Pick a life stage and use the corresponding MER range as a starting point.

**Q: How do I adjust the MER range for my pet?**

Start at the midpoint of the life-stage range. After 2–3 weeks on the new amount, do a body condition score check (palpate ribs, check waist). If the pet is gaining weight, drop toward the low end; if losing, move toward the high end. Adjust by 10–15% per step, not 1%.

**Q: Why is the peak-lactation range so wide (4–8× RER)?**

Milk production scales with litter size and the dam’s body size. A 4 kg queen with 4 kittens sits near the low end of 4–8×; a small hamster dam feeding a large litter sits near the high end. Use the BCS of the dam and weekly weight checks of the litter to narrow the range in practice.

**Q: Does this calculator work for puppies and kittens?**

Yes — pick the growth life stage for the 2–3× factor. Note that growth MER is highest at weaning and tapers as the pet approaches adult size; re-check every 2–4 weeks during the first six months.

## More pet health tools

- [Pet Medication Dose Converter](/tools/medication-dose/) — Convert a veterinary dose rate into a single dose in mg and a liquid volume in mL.
- [Puppy & Kitten Vaccination Schedule Builder](/tools/vaccination-schedule/) — Build a week-by-week vaccination and deworming timeline for puppies or kittens.
- [All Pet Care Calculators](/tools/) — The full tool list, including RER/MER, UVB, feeding frequency, and more.

## References

The RER formula and MER factor ranges come from the WSAVA Global Nutrition Assessment Guidelines and the NRC 2006 Nutrient Requirements of Dogs and Cats, accessed September 2026.

- [Nutrient Requirements of Dogs and Cats](https://nap.nationalacademies.org/catalog/10664/nutrient-requirements-of-dogs-and-cats) — National Research Council, National Academies Press, 2006.
- [WSAVA Global Nutrition Assessment Guidelines](https://wsava.org/global-guidelines/global-nutrition-guidelines/) — WSAVA, 2020. Authority for the 70 × BW^0.75 RER formula and MER factor bands across life stages.
- [Nutrient Requirements of Dogs and Cats (NRC 2006)](https://nap.nationalacademies.org/catalog/10664/nutrient-requirements-of-dogs-and-cats) — National Academies Press, 2006. Source of the 1.2–1.8 MER factor band for adult dogs and cats, and the 2–3× growth factor.

_Educational resource, not veterinary advice. PetGuideCalc — https://petguidecalc.com_