Leg rope

Hey guys. New surfer here. 
Looking to get a leg rope. There isn't much info on the net, my board is 6'5", what size should i get?
It'll just be on small waves, nothing too big...

Looking to get a leg rope. There isn't much info on the net, my board is 6'5", what size should i get?
It'll just be on small waves, nothing too big...