Use a dog food calculator to determine how much to feed your dog, such as the ones available from DogFoodAdvisor.com and MerrickPetCare.com. Determine your dog's ideal weight, which may differ from its current weight, as well as the amount of calories in each cup of the type of food you give your dog. Input those along with your dog's activity level to get an estimated amount.
If you do not want to use a calculator, you can use a formula to calculate the amount by hand. Multiply your dog's ideal weight in kilograms by 30, then add 70 to get the total daily calorie needs. To get your dog's weight in kilograms, divide its weight in pounds by 2.2.
Every dog has a slightly different metabolism, so your dog's needs may vary. Since these are total daily calories, factor in any treats or snacks your dog gets between meals. Learn to recognize a healthy body weight so you can adjust your dog's diet as its metabolism and energy requirements change throughout its life. Avoid letting it become overweight, since overweight dogs are prone to serious conditions such as arthritis, diabetes and hypothyroidism.
Quality commercial diets generally contain a balanced nutrient profile, so feeding the appropriate amount should meet all your dog's nutrition needs. If you prefer to create a homemade diet or your dog has special nutrition requirements due to a disease or other condition, consult your veterinarian.