Also depends on the breeds of chickens.
Leghorns and skinny like chickens are ~3 sqft in coop and 7-8ish sqft in run.
Medium-Large (RIR, BR, etc) are ~4 sqft in coop and 10ish sqft. in run.
XL (Brahmas) I would side with ~5 sqft in coop of 12ish sqft. in run.
Also depends on how often you will let them free range.
I disagree on Leghorns needing less space than Brahmas.
Yes... Leghorns are smaller... but some breeds are much calmer and do not get antsy when confined to a small space. Other breeds when kept in a small space will start feather picking, egg eating, and cannibalistic behaviors.
Size does matter, yes, but I think personality matters MUCH more.