How many cups of dog food in a 30-pound bag. A 30-pound bag of dry dog food holds 480 ounces. If you divide 480 ounces by 5 ounces, which make 1 cup, it gives you 96 cups of dry dog food, which is what you get in your 30-pound bag. How many cups of dog food in a 20-pound bag. By using the same calculations, a 20-pound bag contains 320 ounces, which is equivalent to 64 cups of dry dog food.