Standard Endless Loop Type Bow String
READ CAREFULLY :
A.M.O. RECURVE BOW STRING LENGTH DEFINED: THE ACTUAL PHYSICAL LENGTH OF THE BOW STRING WILL BE 4" SHORTER THAN THE A.M.O. LENGTH.
FOR EXAMPLE IF YOU ORDER A 52" A.M.O LENGTH BOWSTRING THE ACTUAL STRING LENGTH WILL BE ABOUT 48"-49" MEASURED AT 100 LBS TENSION.
General Recurve & Longbow Bowstring Guidelines
As a general rule of thumb most Dacron material ( B-50 ) recurve bowstrings measured out of the package and not under tension will be approximately 4" less than the AMO ( Archery Manufacturer's Organization ) bow length. Longbows are generally 3" less. A Fast Flight Bowstring (FF) which depending on overall length will stretch much less than the standard B-50 strings that can stretch up to an inch under 100 lbs of tension and will look "out of the package" like it is approximately 4 inches or more shorter than the bow. This is the reason you hear people speak about bowstrings being 4 inches shorter than the bow length. Endless loop type string lengths can be adjusted slightly by twisting or untwisting them, this allows for minor overall length variations.
If your unsure of the length needed you can take your old string that has been unstrung from your bow and take the measurement from tip of loop end to the other tip loop end "tip to tip" while stretching it out hand tight with no slack in your string ( make sure the loops are flattened closed and extended out to give the greatest length possible ) assuming this will give you the approximate actual length of your string, now you can add 4" to this measurement anf find your approximate AMO LENGTH.
If you do not have a string on the bow and nothing printed on the bow handle or limb giving you the "AMO" length you can do a little research by trying to contact the bow manufacturer or doing a internet search on how to measure bowstring length, but once again as a rule of thumb the above guidelines are standard and should work in most instances.