How much does your formula fed baby eat?

Courtney💎 • Wife👑 and Mamabear 🐻 Pregnant with #2💛
My son is 9 weeks old (he arrived a couple weeks early and ended up a December baby) and we had many MANY issues breast feeding. Ultimately at 6 weeks we went from supplementing with formula to switching to formula full time. My question is how many oz does your little one eat in a feeding? 
Our little guy takes 4oz at a time every 3 hours or so and if he eats 5 he MIGHT wait 4 hours but he just always seems hungry and I'm afraid to overfeed him. He's currently 24 inches long and around 11.5 lbs