Approximately 30 inches from the ends of the metal catches/hooks.
This may not work for a backpack strap because it is 5 inches from the hook to metal slide on one end and 6 inches on the other when at 30 inches, this can put a metal slide digging into your shoulder unless you can adjust the strap to be longer than 30 inches. Miming a backpack with a strap, it may be able work on a pack for 5'7" me if the length needed is over 33 inches, as the 6 inch clearance would increase to 11 inches (Yes I double checked those measurements).