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RER and MER Calculator for Dogs & Cats
Calculate your pet's Resting Energy Requirement (RER) and Maintenance Energy Requirement (MER) using standard veterinary formulas. Essential for nutrition planning, weight management, and calorie calculations.
Quick Answer
RER = 70 × (body weight in kg)0.75 — the same formula for dogs and cats. For daily feeding, multiply RER by your pet's MER factor: 1.2× for low-activity adults up to 3.0× for growing puppies and kittens.
RER is the minimum calories at rest. MER is total daily calories including activity. Use RER as the floor for weight loss; MER for maintenance.
How It Works
RER Formula
RER = 70 × (weight in kg)0.75
This is the standard veterinary formula for dogs and cats, referenced in AAHA Nutrition & Weight Management Guidelines and WSAVA Global Nutrition Guidelines. RER represents the calories needed at complete rest (base metabolism).
MER Formula
MER = RER × Activity Factor
MER includes calories for normal activity. Typical multipliers:
- Neutered adult, low activity: 1.2×
- Intact adult, moderate activity: 1.4–1.6×
- Active / working dog: 2.0–5.0×
- Puppy or kitten (growth phase): 2.0–3.0×
RER Calculator
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 | MER | |
|---|---|---|
| Full name | Resting Energy Requirement | Maintenance Energy Requirement |
| What it measures | Calories at complete rest | Total daily calorie need |
| Formula | 70 × (kg)^0.75 | RER × activity factor |
| Typical range (20 kg dog) | ~639 kcal/day | 767–1,150 kcal/day |
| Use for | Weight loss baseline; hospitalized patients | Daily feeding guidance |
| Never feed below? | Yes — RER is the minimum floor | N/A |
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.
| Weight | RER (kcal/day) | MER Low (1.2×) | MER Moderate (1.4×) | MER Active (1.8×) |
|---|---|---|---|---|
| 5 lbs (2.3 kg) | 131 | 157 | 183 | 236 |
| 10 lbs (4.5 kg) | 218 | 262 | 305 | 392 |
| 20 lbs (9.1 kg) | 366 | 439 | 512 | 659 |
| 30 lbs (13.6 kg) | 497 | 596 | 696 | 894 |
| 44 lbs (20 kg) | 639 | 767 | 895 | 1,150 |
| 50 lbs (22.7 kg) | 727 | 872 | 1,018 | 1,309 |
| 66 lbs (30 kg) | 848 | 1,018 | 1,187 | 1,526 |
| 70 lbs (31.8 kg) | 935 | 1,122 | 1,309 | 1,683 |
| 100 lbs (45.4 kg) | 1,218 | 1,462 | 1,705 | 2,192 |
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.
kcal/day by body weight. Note the flattening curve — larger pets need proportionally fewer calories per kg.
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:
| Dog Status | MER Factor | Notes |
|---|---|---|
| Neutered adult, low activity | 1.2 × RER | Indoor dogs, minimal exercise |
| Intact adult, moderate activity | 1.6 × RER | Regular walks and play |
| Active/working dog | 2.0–5.0 × RER | Herding, hunting, sled dogs |
| Puppy (0–4 months) | 3.0 × RER | Rapid growth phase |
| Puppy (4–12 months) | 2.0 × RER | Continued growth, moderate pace |
| Pregnant (last trimester) | 1.8–3.0 × RER | Increases with litter size |
| Lactating | 3.0–6.0 × RER | Depends on litter size and stage |
| Weight loss | 1.0 × RER | At target weight, vet supervised |
| Senior dog | 1.0–1.4 × RER | Reduced metabolism, adjust individually |
Cat MER Activity & Life Stage Factors
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.
| Cat Status | MER Factor | Notes |
|---|---|---|
| Neutered indoor cat | 1.0–1.2 × RER | Sedentary indoor lifestyle |
| Intact adult cat | 1.2–1.4 × RER | Slightly higher metabolism than neutered |
| Active outdoor cat | 1.4–1.6 × RER | Hunting, exploring, temperature regulation |
| Kitten (0–4 months) | 2.5 × RER | Rapid growth phase |
| Kitten (4–12 months) | 2.0 × RER | Continued growth, slightly less than young kitten |
| Pregnant cat | 1.6–2.0 × RER | Increases through pregnancy |
| Lactating cat | 2.0–6.0 × RER | Depends on litter size, free-feed recommended |
| Weight loss | 0.8 × RER | At target weight, vet supervised — never fast a cat |
| Senior cat (11+ years) | 1.0–1.1 × RER | Reduced activity, monitor weight closely |
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.
Important: RER/MER Are Starting Points
RER and MER calculations provide a starting point for calorie planning. Every pet is different — monitor your pet's weight and body condition score every 2–4 weeks and adjust portions accordingly. Consult your veterinarian for personalized feeding plans, especially for weight loss, pregnancy, growth phases, or medical conditions.
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.
References
- AAHA (2021). Nutrition and Weight Management Guidelines for Dogs and Cats. American Animal Hospital Association.
- WSAVA (2021). Global Nutrition Guidelines. World Small Animal Veterinary Association.
- Hand, M.S., et al. (2010). Small Animal Clinical Nutrition, 5th Edition. Mark Morris Institute.
