I use Bonnie Hunters border method. There is NO measuring involved and my borders come out perfect every time. I just fold the quilt in half, lay my border strips on the fold, smooth out and cut even with the end. If I am working with a larger quilt, I will start at one end and pin every foot or so and fold it up as I go along until the other end is on the table. I think it's more accurate that way. The trick is to SMOOTH and not stretch the fabric as you go. I usually pin the center and ends first when applying the borders. The I pin periodically between those.
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