Cats like dogs vary in size. A small cat may weigh 6 lbs, while a large one may weigh 20, so of course their food requirements will be different. As well as size, activity level and age will influence how much your cat needs to eat.
Indoor cats may be less active than outdoor cats, and some outdoor cats may catch their own prey to supplement what they eat at home, two factors you will want to keep in mind when determining if your kitty is getting enough to eat.
A good guide though is to know the average adult cat eats about 150 – 200 g/day. Kittens eat more than this because they are growing so quickly. Rest assured that when they are adults their food consumption will decrease.