Freezing milk - how many ounces in a bag?

ALF
How many ounces do you freeze in each bag?  I started off freezing 4 oz. to a bag but wondering if I should bump it up as my LO sometimes will eat 5-6 oz. of fresh pumped milk at a time when I give him a bottle.  Also how do you know how much milk to send to the babysitter since I feed on demand right now while on maternity leave.  My guy is 8 weeks old.