RER and MER Calculator for Dogs & Cats

How It Works

RER Calculator

What Is MER (Maintenance Energy Requirement)?

MER, or Maintenance Energy Requirement, is the total number of calories a healthy pet needs each day to maintain its current weight, including the energy used for normal activity, digestion, and keeping warm. It builds on RER: you take the resting figure and multiply it by an activity factor that reflects your pet's life stage, activity level, and reproductive status. In short, RER is the floor and MER is the real daily feeding target.

Pet owners usually need a MER calculator when deciding daily portions, comparing what a food label recommends against your pet's real needs, planning for a growing puppy or kitten, or adjusting after spaying or neutering drops calorie needs. Because a MER that is even 10 to 20 percent too high leads to steady weight gain, getting this number right matters.

RER vs MER: What's the Difference?

RER (Resting Energy Requirement) is the calories a pet burns at complete rest, breathing, circulation, organ function, and cell maintenance. MER (Maintenance Energy Requirement) is the total daily calorie need, adding activity, digestion, thermoregulation, and life stage demands on top of RER.

RER Quick Reference Table

Common RER values by body weight. Find your pet's weight and see their resting calorie needs instantly. MER columns show daily calories at different activity levels.

Values calculated using RER = 70 × (kg)^0.75. Use the calculator above for exact results with your pet's specific weight.

RER by Body Weight: Reference Chart

The RER curve shows how calorie needs scale non-linearly with body weight. A 40 kg dog does not need twice the calories of a 20 kg dog, only about 1.6×. This metabolic scaling (the 0.75 exponent) is why the formula is more accurate than simple per-kg estimates.

Dog MER Activity & Life Stage Factors

For dogs, MER multipliers vary by activity level, life stage, and reproductive status. These are standard veterinary guidelines used by the AAHA and WSAVA:

Cat MER Calculator: MER Factors for Cats

This works as a cat MER calculator too. To find the MER for cats, take your cat's RER and multiply it by the life stage and activity factor below. This is the same Purina-style MER approach vets and the Purina body condition tools use: RER first, then RER times a feline factor. Cats generally have lower activity multipliers than dogs. Indoor cats are particularly prone to obesity because their energy expenditure is much lower than outdoor cats.

To turn these calories into cups or cans of a specific food, use our Cat Feeding Calculator, or get a full calorie plan with the Cat Calorie Calculator.

RER Calculator for Cats

The RER formula is the same for cats as for dogs, RER = 70 × (kg)^0.75, but cat-specific considerations matter:

• Indoor neutered cats are especially prone to obesity. Use 1.0–1.2× RER and monitor body condition score every 4–6 weeks.
• Never fast a cat. Cats that go 24–48 hours without food can develop hepatic lipidosis (fatty liver disease), which can be life-threatening. The weight loss floor for cats is 0.8× RER at target weight, always vet supervised.
• Outdoor cats expend significantly more energy on thermoregulation and activity, use 1.4–1.6× RER.
• Senior cats (11+ years) may actually need more protein and calories than middle-aged cats as muscle mass can decline; monitor weight monthly.

For a complete daily calorie plan for your cat, use our Cat Calorie Calculator, which accounts for food type, brand, and body condition score.

RER for Puppies & Kittens

Growing animals need significantly more energy than adult pets of the same weight. The RER formula still applies, but MER multipliers are much higher during growth phases.

RER for Puppies

Puppies aged 0–4 months use 3.0× RER, they're in rapid growth and need triple their resting energy. From 4–12 months, this drops to 2.0× RER as growth slows. After 12 months (or when they reach ~80% of adult size), transition to the appropriate adult multiplier.

Large and giant breeds (e.g., Great Danes, Mastiffs) should be kept on the lower end of their growth-phase MER and fed breed-appropriate puppy food to avoid overly rapid bone growth, which can contribute to orthopedic disease. See our Dog Calorie Calculator or breed-specific weight calculators for growth targets.

RER for Kittens

Kittens aged 0–4 months use 2.5× RER. From 4–12 months, this drops to 2.0× RER. After 12 months, most cats settle into the neutered indoor adult range of 1.0–1.2× RER.

Kittens should be fed kitten-specific food (higher protein, higher fat, plus taurine supplementation) during growth phases. Free-feeding is generally acceptable for healthy kittens since they tend to self-regulate until around 6 months. For a full calorie guide, see our Cat Calorie Calculator.

For a complete daily calorie plan based on your pet's specific factors, use our Dog Calorie Calculator or Cat Calorie Calculator. For weight management, see the Dog Weight Loss Calculator or Cat Weight Loss Calculator. For puppy nutrition, see the Puppy Calorie Calculator.