Do chickens need store bought feed all day long?

[Willow's Meadow]

My chickens live inside of my barn at night. In the day I let them outside and I bring there food and water out with them. I can't leave it inside because I have other animals, and cement floor and I don't want them wandering in and out---making a mess and getting into un safe chicken parts of the barn. But there feed seems to be empty by the end of the day(I give them about half of a 10 lbs. feeder full and there are 17 chickens.). My first question is...how much feed does a flock of 17 2 months old usually eat? I don't measure it...but I wanted to know if they are ACTUALLY eating it all day or it is being wasted some how.