I know your bottle feeding, and that's okay. I'm breast feeding mine, and when I nurse, there isn't any way to know exactlt how much he's getting. So I just follow his cues. When he acts hungry I feed him, and I let him stop when he want to stop. But I also watch his diapers. If he's having plenty of wet and dirty diapers I know he's getting enough.
I think the same rules can apply to bottle feeding. Don't worry so much about amounts... just follow your son's cues. If he's acting like he's hungry, feed him. And when he stops eating stop feeding him. Your baby knows what his feeding needs are better than any book or doctor out there. Just follow your baby's needs on this one. And watch his diapers. If he's peeing frequently, that means he's well hydrated, and if he's having dirty diapers, that means his digestive system is getting nutrients. Just relax and trust your baby and your mama instincts.
P.S. There was an earlier recommendation for the Babywise book. Be very careful about this as the AAP has recommended against their techniques and has found that they are linked with dehydration and failure to thrive.