Best answer is, buy the best food you can afford and read the label on the package. It is your best guideline. If after a couple of weeks, you dog looks like it gained an unwanted pound or two, slightly decrease the amount. If it looks like it has lost an weight that it needs add a little bit. I have had several dogs and have adjusted for most.
Nutritional and caloric needs vary from dog to dog so it’s hard and technically unsafe to provide a specific number, although the general consensus is about ¾ to a cup per day for a 10-pound dog. I’d say check the food label and see how much to feed your pup based on the manufacturer’s recommendations. The same cup from one brand doesn’t necessarily provide the same calories as one cup from another.
Given that every dog has different needs, levels of exercise, and age, you’d also want to rely on common sense for this matter. Of course, a standard indoor toy dog doesn’t need to eat as much as one that gets plenty of exercise. You’d want to monitor your dog’s weight and watch out for signs of over or underfeeding. Ideally, you’d want your dog’s ribs to be palpable, but not visible.
If you need help finding the appropriate food for your small pup, head on over to https://thedoggypedia.com/dog-food-small-dogs/ for some of the best recommendations.