I was told by a LQS owner to always buy three yards of a fabric if it does not have a project to go into, but it is for your stash. However, I still seem to be a 1/4 yard short, when I go to use it. I don't think there is a magic yardage. If you like a piece buy plenty. If you come across a sale, stock up on background fabric. Buy six yards of a light colored tone on tone, (white or cream) and then you will have plenty for what ever you need, and you will always use it in something. I inherited my mom's stash, and she had bought six yards of a white on white when our LQS went out of business. I have used it as a background for three quilts and still have plenty.