Dog & Cat Calorie Calculator (RER and DER)
Calculate Resting Energy Requirement (RER) and Daily Energy Requirement (DER) for dogs and cats. RER is the calories needed at rest in a thermoneutral environment; DER adjusts for activity, life stage, and reproductive status.
Species
Body weight
Life stage / activity
How to use this tool
The formulas
RER = 70 × (body weight in kg)0.75 - the metabolic-weight calculation. Works for patients between 2 and 45 kg. For very small or very large patients you can use the linear approximation RER = (30 × kg) + 70.
DER = RER × life-stage factor. Typical factors:
- Adult, neutered: 1.6 (dog), 1.2 (cat)
- Adult, intact: 1.8 (dog), 1.4 (cat)
- Weight loss target: 1.0 × RER for ideal body weight
- Weight gain target: 1.7–2.0 × RER
- Hospitalised patient: 1.0 × RER (use current weight)
- Growth (puppy <4mo): 3.0; (4mo–adult): 2.0
- Growth (kitten): 2.5
How to apply it
Convert the DER to grams of food using the kcal density listed on the diet's label (most labels list kcal/cup or kcal/can). For weight loss, target the ideal body weight, not the current weight, and recheck every 2–4 weeks.
Frequently asked questions
How are RER and DER calculated?
RER (Resting Energy Requirement) = 70 × body weight (kg)^0.75. DER (Daily Energy Requirement) = RER × an activity / life-stage factor. Typical multipliers: neutered adult dog 1.6, intact adult dog 1.8, weight-loss dog 1.0, hospitalised patient 1.0-1.4, puppy < 4 months 3.0, lactating dog 4-8 (varies with litter size).
What is the difference between RER and DER?
RER is the baseline caloric need at rest - just enough to keep an inactive animal alive in a thermoneutral environment. DER is the real-world target that accounts for activity, growth, lactation, illness, and recovery. You feed to DER, not RER (except in some hospitalised cases).
Why is the kcal value lower than what the bag of food recommends?
Bag feeding guides assume an "average" intact, active adult and almost always overestimate. Calculated RER/DER is far more accurate for an individual patient. If your patient is gaining weight on the bag's portion, that's why.