Working/pumping moms...

Elizabeth • Cleveland, Ohio - Christian - In need of mom friends
How do you decide how much milk to put in each bottle for your child's caregiver while you are at work? 
My son is almost 5 months old. When I'm home, he nurses every 2-3 hours during the day and about every 3-5 hours during the night.  I don't know how much milk he is actually getting, of course. I usually fill each bottle to 3 ounces, but it seems like now that he is getting older, he should be drinking more milk less often. How do you figure out how much to put in your baby's bottles?