The measasure is the outer circumferance of the belt, and Sew Classic has a pdf page on how to measure correctly with a string. I should really not advice you since I had to order three times to get correct belt for my beige Singer 201K23. There is a bit of room for adjustment but it's not much. Take my abillity to measure correctly into account, but I would go for 14 1/2 inch since measure is the outer circumferance, and I'm guessing you had a string into the groove of the pulley and hand wheel? I still lean towards the black V-belt when I can find them in the correct size, but will go for lugged belts when needed. Both types are technically V-type belts; and fits the groove as they should.