When you wash fabric, you have to allow extra for shrinkage. If you don't pre-wash, you should be able to count on having accurate measurements whether it is in factory pre-cuts or what is cut at the LQS -- and I have found that I can't count on any of that. I assume I can get 34"x40" of usable frabric out of 1 yard of fabric. Sometimes I get more and am pleasantly surprised. It is frustrating that the work today is so sloppy.