I heard that a laying hen should get 75g of food a day. I have never measured mine, I figured it out by myself. I have a tub and I just work out how much they eat of it and then that's what I give them.
They should eat about a 1/4 lb for a lightweight breed or 1/3 lb for a heavyweight breed, per day. I don't remember what the amount is for a banty, sorry.
I just leave food in the feeder all the time and they eat what they need. They prefer to eat what they can forage, so it's never that much. It's good to have a general idea, though, for planning or in case you have pests stealing food.