I havent measured it,but I did try to fit one to a V8 tyre and it was too tight and ripped,this was when I found out there are 2 sizes of cover!
ianp6man will probably know as he is selling some at the moment!!
I would imagine that the repro's about now would be made to fit the larger tyre,so will fit the smaller one as well,but will be a little on the loose side,not enough to worry about though!