Couple of thoughts here. First, do you have a reasonably large piece of the same fabric that you can tear to see if the design is printed on grain? If so, once tested I would then tear my border lengths with a tad extra on width to trim torn edges. If you are looking to get a specific section of the directional print lined up with your quilt, I would also do as Terri D suggests re measuring. But instead of cutting, if the design is printed correctly relative to the grain of the fabric I would still tear. If the design is printed off-grain, then I would follow Terri D's recommendations.