not being a math wizard, here are my thoughts..whatever the width of the binding you want x 3 (and a little more)..that way you would attach with 1/3 the width, fold up (another 1/3) and over (the last 1/3), the little more would allow you to "catch" when SID. You would have to be very exacting in stitching to do this :) that's why I start on the back fold to the front and stitch like everyone has suggested.