I measure 3 time. Once on each side (doing the sides here) and once thru the middle. Average these measurements. This is the figure for your side borders. Once you have sewn them on than measure again, across the top, the bottom and thru the middle. (This is assuming you are not mitering, a whole other subject.) Than I also sew with a walking foot with the body of the quilt on the bottom. Hope this helps.
