I asked this question before on a different thread, Sheldon is 15 weeks today, when he was 10 weeks (2.4 lbs) the vet suggested the amount of 1/8 cup of dry food 3 times a day.
At 15 weeks 1/2 a cup is not enough, he has a vet appointment this morning so I'll ask her how much should he be eating.
Good luck and congrats on the new puppy
Maggie