Look around at some of the mfg websites. Hennessy Exped is 52" wide, Warbonnet Traveler is 65" wide. ENO Single is 55" and the ENO Double is 74". They're all over the place.
It's a matter of fabric and preference. Some want narrower because it's less weight. Some want wider because it's easier to get a good diagonal going. That also depends on your height.
There's certainly no "one size fits all."