In a "tedious" post, Kathyl remarked that she really dislikes measuring for borders. I wonder how she does it, and how others do that. Here is what the Quilting Divas (my Quilt of valor Bee) does for the twin size QOV we make. We recently did the same method for the Relay for Life queen size quilt. Other quilters have other methods, but this has been successful for us for over two dozen quilt tops.
We make sure the quilt is pressed and flat, then smooth it our on a clean sheet on the floor. We usually cut the side borders first. We cut those to desired width and add several inches to the 'anticipated' length. Then we lay both strips, stacked, through the middle of the quilt, aligning with a seam for accuracy. Of course we pat and smooth to be sure it is straight, then pin the borders to one edge of the top, with a few inches extending. Using a rotary cutting equipment, we cut the excess and KEEP the pins right there. We double check that all is still straight and smooth, and repeat pinning and cutting on the opposite edge. After we sew those borders to the sides, we press the borders out and repeat procedure for the other two borders. Note: this works for miter, butted, or corner squared corners. Don't forget: measure twice, cut once!
PAT in VA/USA