L., think about it this way... if you were still breastfeeding, would you feed him a certain number of ounces or feed him until he's full? Obviously, until he's full. Babies don't overeat, so I'm not sure what your concern is... is it that he'll he too much and then spit up? Well, again, think about it- he has reflux because the valve in his throat isn't fully developed, not because his tummy isn't big enough. His tummy still wants to be fed after you take his bottle away, even if he spits up after he eats his fill. My son ate well and would spit up at least 4 times after each feeding. I became very adept at catching it and such. He always wore a bib (for the first year) and I always had a burp rag next to him. He was always thriving and growing. I would never underfeed him (if he's crying and sucking on you after eating, he's underfed) even if I was concerned about him spitting up. My son also projectile vomited sometimes (he may have eaten a little too much then or I didn't get out the burps). I never had him on meds or any of that. Almost all babies spit up- it's normal. Just make sure you get those burps out (after a couple of ounces if you're concerned about spitting up). The air in their bellies will overfill it, when added to the formula. Oh, and we used Dr. Brown's bottles... they helped a lot with the evening gas problems.