Pumping/Stashing for Breastfed Baby

Rachel
If you're breastfeeding, how much does your baby take in s bottle, and at what age?
I'm trying to build a little freezer stash but I'm not sure what quantity to freeze it. Right now I have 3, 3.5 and 4 oz bags frozen, but when we go out my little one will happily suck down 4 oz and look for more. I don't know how much he would eat if he was getting bottles every feed, but I don't want to wait to pump 4 oz for each bag, as I usually get 1-1.5 oz per breast per pumping session. 
Just wondering how much everyone else's baby eats 😝
My little guy is currently 6 weeks!