I must own pigs not poultry! Mine free range and go through lots of veggie scraps and about 20LB of pells and some other grain du jour each 4-5 weeks. They do slow down in the summer. I have 7 chickens, 2 ducks and 6 geese. I must say I don"t waste any food and get valuable poops and goose juice for the garden!
I have 75 (I think) bantam chickens that are all free rangers, except for broodies, mamas with chicks, and chicks with no mamas, and I feed about 100# a month. Now, on the other hand, my 8 ducks, which are also 'free range' eat about 100# a month also...
That figure is most likly based off your commercial leghorn layer. A thin light white bird who's adult weight is 3 lbs and lives in a climate controled cage it's whole life. Don't be surprised if your back yard type who weighs 6 lbs eats 2-3x more on a regular basis. I am curently going though 50lbs of feed a month with 8 standards (about 6 lbs each) and 6 banties (about 3 lbs each). However, they get to range as far as the eye can see from sun up to sun down. Cooped up they'd probably eat more than 2-3x that, plus the fact that it has only recently gotten colder. I anticipate feed consumpton to 2x for the winter. That said, with the average 14 birds eating 50 lbs a month, if you only wanted three, a 50 lb bag would probably last the urban 3 chicken user 3-4 months on a mix of standard and banty birds.