I do what Lana does, Owen does knows when he is hungry and for how much. As far as how much that is, differs from day to day. This is what I offer on a typical day:
B
Cereal, slice wheat toast with butter, and some fruit cut up - like 1/4 apple or whatever - 4-6oz milk
L
1/2c pasta and red sauce or 1/2 grilled cheese or 1/2c soup or leftovers from the night before - 4-6oz milk
Snack
grahams or yogurt or apple sauce or cheese and crackers
D
meat, 1/4c veg, 1/4c starch - 4-6oz milk
He has a sippy of water (8oz) which I filled probably 4-6 times a day - whenever he brings it to me empty lol. He is big too, 29lbs and 34inches tall. Most often he will eat like a horse one day and then practically nothing the next.
I think we are born knowing exactly what we need and don't need. I think sometimes that "Im full, Im hungry" part of us can be easily over-ridden by our care-givers when we are little. Therefore, I believe letting Owen eat til he says he is done - be it all the food and then some or two bites - is important, as is offering healthy snacks when he appears hungry.
HTH!