The "thumb rule" is 1/4# per bird, per day. For an average adult chicken in average conditions. None of us have that theoretically average chicken - its like having an average 2.3 kinds in your family... But it gives a good starting point.
If you have Cx or other "meaties", you expect they will eat (a lot) more. Small breeds may eat much less. and there's a whole spectrum in between. Similarly, low nutritional value low energy feeds will be consumed in greater quanitity, while high energy nutrient dense formulations will be consumed less... Time of year can have an impact, activity level, state of molt... Cage or contained run kept eat more than those who can suppliment by free ranging....
So your question doesn't have a clear answer - but the guideposts above are good estimates as a starting point for your expectations. My flock (see sig) eats 300# per month right now, but they free range 24/7, I'm in a forgiving climate, I've worked on my pasture quality, and my birds have most of 2 acres of pasture plus another three of underbrushed woodland. Come February when my pasture provides very little, I expect their consumption will have climbed closer to 375# per month.
