Mazuri recommends two tablespoons of pellets per chinchilla per day. Some will eat a bit more than than, some a bit less. Patty can eat twice as much as that, lol.
Generally, I go by that 2 tblsp. rule every day. My pair get 4 tblsps in their big bowl, and Patty gets a double serving, and then my other two single (normal sized) girls get 2tblsps per day in their bowls.
I always dump the old pellets out before refilling, and that way I know they are eating fresh pellets, without any poopies or nasty pee in it.
Yes, sometimes they get goofy and pee in the pellets. <eyeroll>