How much baby food and rice cereal should I be feeding my son?

Okay, he's been eating for a few weeks now, and he's a hefty guy. I feed him all three meals a day now. My question is really about the rice cereal. The directions on the box say for their first feeding use 1tbsp and whatever amount of milk or formula. Well, we are WAY past him eating it for the first time, and he mashes on all the other foods, he'll eat the whole container most of the time. I just don't know how much rice cereal to make him in the morning. Should I just eyeball it? Feed him until he turns his head and doesn't want anymore? Help me out here.