As in most things related to sailing, "it all depends." In this case, it depends on the size of your headsail's foot, the type of furler you have, and the diameter of the furling line. I typically put 30 turns on the furling line before hoisting my 150. I put on 25 for my 130, etc. If that doesn't work for you, that is, it's too many or too few turns, just take your headsail sheets off and wind or unwind the sail by hand until it's right. I also use and indelible marker to place a mark on the furling line where it exits the drum to show when I've got enough turns on the drum. One mark for the 120, two for the 150. Whatever works, works.