5 yards x (44"/108") = 2.04 yards of backing fabric, or very slightly over 2 yards.
Depending on the cutting pattern, 2 yards might be enough, but I would probably get 2 1/4 yards, just to be safe.
Good luck!
PS: I just checked out your profile; your quilt inspectors are fabulous!
Last edited by Jennifer23; 01-28-2014 at 05:21 PM.