How much does your formula baby eat?

Hi there! I am having to supplement with formula because my supply isn't keeping up with my sons demand and sometimes he doesn't want to latch. He is 3 weeks old and will take anywhere from 2-4 ounces of formula every 3-4 hours (4 ounces if he doesn't breastfeed prior). Occasionally he has taken 6 ounces over a 2-3 hour time span). How much does your formula baby eat and what age is he/she?