Dave, I don't mean to butt in here, but Dan is giving good advice. The old "rule of thumb" has bee 4" shorter than a recurve for as long as I can remember, BUT it won't apply to every bow. AMO specs are 3" shorter, longbow or recurve, but (obviously) a lot of bows don't go by that either. I've seen string lengths vary (on recurve bows) from 2.5" shorter than the AMO to 6" shorter; on longbows from 1.5" shorter to 4" shorter.
String makers can vary also--one may send you a string that's 58" after it's had 300# of tension applied; another only puts 100# on it, and another may not pre-stretch at all--that's going to make a big difference once you get the string shot in.
Measureing the string isn't a fool-proof guarantee, but in my experience it's the best way to get the right length the first time.
Chad