Why Is My Cat Always Hungry?
Cats are typically grazers who snack throughout their waking hours, so if your cat finishes their meals and asks for more, this may indicate a problem, ranging from boredom and medical causes to simply needing more calories. Different commercially available foods have different caloric contents, and you can typically find a guide on the food container.
If you have a cat that is ALWAYS hungry, then this video can help you.