This varies greatly depending on size, age and breed. 6oz of feed is a pretty close estimate. If you are losing feed overnight, that is pretty easy to check on. Frankly, I detest feeding rodents. I use a ration management system, but it requires much more attention to detail than 24/7 availability.
I feed heavy in the early am, usually before 6 am. They take virtually all day, pecking at it, to eat it all and they get all they want. At 4 pm, if they have managed to finish off the morning feeding, I'll feed them a lesser quantity, as I want them to clean it up before going to roost at 8 pm. There is then no feed for the night time visitors. This method also means I do not need to physical pull feeders each night and re-place them in the early am. It might be worth a try to see if your suspicions are correct.