I know that many say to use the center of the quilt for your border measurements, but I use the two sides and the center, then I average those. The average is what I use to cut my borders. Also, if you cut your borders WOF. it will ease better. I just put borders on a quilt this morning, and I cut my borders length of fabric. They weren't as easy to "ease". Be sure to mark the center of the quilt side, and the center of your border strip... pin the center and the two sides, and ease the rest in. After all, the quilt is going on the bed, not on the wall. And no one will ever see that your sides don't match perfectly!
