Ready to freeze some milk! How much in each bag?

I think I'm finally ahead enough of my boy's demand to start freezing some milk. What's a good quanity in each bag to freeze? Right now he mostly eats in 2 ounce sessions but I was wondering if I should put 4 ounces in each bag in order to save bags and do less defrosting later on. Or should I try to fill the bags? FTM, I have no clue what to do haha!