I saw it in 1977, at a theatre in the town where I grew up in England. For being a a fairly small town, the theatre was fairly large, it was subsequently converted to two theatres by simply splitting it right down the middle. TL;DR, it was a fairly sizeable screen.
The one memory I have was of the opening scene, where the first ship seen is Princess Leia’s, and my thoughts were “Man, that’s a pretty good sized ship.” Little did I know what was coming seconds later. 😃