I always guess how many WOF I need for the sides. Usually I need almost 2 strips per side. I measure through the center with that strip and gently smooth it out. I cut that strip to that size, I then lay it on top of the other strip and cut that one the same size. I mark the center of the two strips and fold each end to the center pin, mark with a pin. I do the same to the quilt and pin them together. Sew those borders on, press and measure with one border strip and repeat above. My borders always come out perfect.