The easiest way I found to determine a belt size is to find a sacraficial belt that is much longer, with the correct top width and cut it. Put the alternator adjustment, or whatever you are trying to fit a belt to, to it's half way point. Run the cut belt around the pulleys and mate the ends. One end will cross over the other, and put a mark on the spot where the belt is at it's tightest point. If you measure the length you end up with, that's the size you'll need. It sure goes alot quicker doing it compared to typing it.