An average laying hen will consume about ¼ pound of feed per day, depending on factors such as size of the bird, weather conditions, and level of productivity.
But, you're going to want to make sure that they're on the full feeding method. Full feeding refers to offering a constant supply of feed at all times. Typically, when hens are restricted from consuming the amount of feed they desire, egg production will cease. Food out for them all day, every day - leaving the feeder out at all times. I have 20 chickens and we go through a 50 pound bag in about a month, and they free range a lot. Most days, almost all day.
In the spring and summer they will probably eat significantly less feed than in the fall and winter if they have access to range, but they will still need that base feed to keep them going. In the winter especially they need calories to keep them warm, and in the fall they need protein because they will be molting and renewing their plumage. In the spring and summer they are usually laying their peak of eggs, so all those calories go to help produce the eggs and keep them in good condition while they produce.
If you use a treadle feeder you will be amazed at how much less feed you'll go through.