Agree with Sadiemae. It depends on the pattern. But off the top of my head
I would say at least 2 JR for a Queen. I would recommend choosing the
pattern first. Some patterns have a lot of background fabric so you don't
need as much. Also, will you have borders or not?
Search for Jelly Roll in the picture section or through google image.
Also, check modabakeshop.com. They have lots of patterns there.