Hong Life CalculatorsUnderstanding the dog and cat daily food calculator — concept and principle
How much should your dog or cat eat each day? This calculator follows the method veterinarians use: it estimates the resting energy requirement (RER) from body weight, multiplies it by a life-stage factor to get the daily energy need, and converts that into grams of your specific food using its energy density.
How it is calculated
- RER (kcal/day) = 70 × (body weight in kg)^0.75.
- Daily energy (MER) = RER × life-stage factor (for example 1.6 for a neutered adult dog, 1.2 for a neutered adult cat, 3.0 for a puppy under 4 months).
- Food per day (g) = daily energy ÷ food energy (kcal per 100 g) × 100.
Body weight is in kilograms. Energy density is usually printed on the label as kcal per kg or per cup; divide kcal per kg by 10 to get kcal per 100 g.
The principle
Energy use does not rise in direct proportion to body weight. A larger animal has less surface area per kilogram and a slower metabolism per kilogram, so its needs scale with weight to the power 0.75, a relationship known as Kleiber's law and expressed as "metabolic body weight". RER is the energy needed at rest in a comfortable environment. The life-stage factor adds the extra energy needed for normal activity, growth or reproduction, and lowers it for neutered, inactive or overweight animals.
Worked example
- Inputs: 15 kg, neutered adult dog (factor 1.6), food 370 kcal per 100 g.
- Metabolic weight: 15^0.75 = 7.622.
- RER: 70 × 7.622 = 533.5, shown as 534 kcal.
- Daily energy: 533.5 × 1.6 = 853.7, shown as 854 kcal.
- Food: 853.7 ÷ 370 × 100 = 230.72 g per day, which you might split into two meals of about 115 g.
| Body weight (kg) | Daily energy (kcal) |
|---|---|
| 3.75 | 302 |
| 7.5 | 508 |
| 11.2 | 688 |
| 15 | 854 |
| 18.8 | 1,009 |
| 22.5 | 1,157 |
| 30 | 1,436 |
How to read the result
Treat the result as a starting point. Weigh the food with kitchen scales rather than a cup, and check your pet's weight and body condition score every two to four weeks. If the animal gains weight, reduce the amount by about 10% and recheck; if it loses weight or looks thin, increase it. Treats count too: a common guideline is to keep them to about 10% of daily calories.
Common mistakes
- Mixing kcal per kg and kcal per 100 g, which makes the amount ten times wrong.
- Measuring dry food by volume; cups vary a lot in weight.
- Forgetting treats, chews and table scraps.
Frequently asked questions
What is the difference between RER and MER?
RER is energy at rest; MER (maintenance energy requirement) is the daily need including normal activity, found by multiplying RER by a factor.
Why not use a simple linear formula?
The linear shortcut 30 × kg + 70 is sometimes used for animals of about 2 to 45 kg, but the exponent formula fits small and large animals better.
How do I feed for weight loss?
Your vet usually bases calories on a target weight with a lower factor and monitors progress every few weeks.
Sources: National Research Council — Nutrient Requirements of Dogs and Cats (National Academies Press, 2006) · WSAVA Global Nutrition Committee — Global Nutrition Guidelines