How do I calculate my dog's daily calorie needs?

First, weigh your dog accurately in kilograms. Second, raise that weight to the power of 0.75, which most calculators or a simple scientific calculator app can do, and multiply the result by 70 to get resting energy requirement.

Third, multiply resting energy by an activity factor suited to your dog, roughly 1.2 to 1.4 for sedentary, 1.6 for average, and 1.8 or higher for active or working dogs, to get the daily calorie target.

For a 15kg dog, weight to the power of 0.75 is about 7.62, so resting energy is 70 times 7.62, around 534 kcal. Multiplying by 1.6 for average activity gives a daily target of roughly 855 kcal.

If that dog's food provides 380 kcal per 100g, dividing 855 by 380 and multiplying by 100 gives about 225g of food a day.

Treat the result as a starting point rather than a fixed answer, and adjust up or down by about 10 percent based on how your dog's body condition responds over two to three weeks.

A food calculator tool can do this math for you automatically once you enter your dog's weight and chosen food, which is faster than working through the formula by hand each time you need to check it, and reduces the chance of a small arithmetic slip along the way somewhere in the process.