Usually 4" for recurve and 3" for longbow until recently ....new standard is that AMO bow length is 3" longer than AMO string length. Which confuses things.
Best to measure what bowyer recommends but my 62" Browning Explorer has a 56" endless loop on it and has not been strung in many years so may end up being closer to 58" when settled and stretched.
Just be sure to use Dacron whether it is endless loop or flemish twist. If going to shoot it I would get a flemish twist first...even if solid colors so you can twist it up and down to find the correct brace height for your bow and shooting and then can make or buy a new endless loop later.
Bearbowman can help you figure it out even though he typically makes them for Bear recurves.
http://www.flemishstrings.com/