Cat weights vary greatly. The best way to tell if your kitten is at a healthy weight is to run your hands down it's ribcage. You should be able to feel the ribs, but they should not be protruding and you shouldn' have to 'dig' to feel them. Many cats have a 'fat pad' or the greater omentum that hangs somewhat low between their hind legs. This is not a sign of being oveweight. This is a normal part of some cats' anatomy. The easiest thing to do with cats is to 'free feed' them. Keep dry food down and available all the time, and if you want to feed canned, you can give them a can in the evening or morning, or 1/2 can twice a day. Cats are not overeaters by nature, and they prefer to graze throughout the day in most cases.
If I can help further, feel free to ask!
Feline Healthcare
16 yrs health care mgmt & issues relating to cats, reproductive issues and multicat environments