How much ventilation size is sufficient or adequate for chicken buildings?

Ventilation for animals is as important as it is for humans. I have found in some literature how estimations are made for human dwellings, taking into consideration the number of bedrooms, orientation of the building and wind speed. But I have not been able to find the area of windows that can be sufficient for a given number of chickens (broilers or layers). Can someone help me with a clear cut formula?

I don't know about a formula but generally chickens need a lot more ventilation than people. They don't do well with wet, but aside from that they can cope with drafts fine. They are evolved to root outdoors in the branches of trees after all.