Such a hard question to answer! I guess if I find a solid that is great quality at a great price, I would buy enough for a backing...if it was a primary color like black or white I would try to buy as much as I could afford. Buying prints is different as it has to be either a primary print fabric and everything will work with it....or it is a blender to work well with others....a primary print I would buy enough for 1 quilt and that may be 2/3 yards....a blender print will be as much as I can afford, as it will work into many different types of quilts. With all my fabrics/projects, I now do not save the small pieces. I cut everything that is less than 1/2 yard down....starting with 10" squares and going down to 2.5" strips. I end up with the start of great scrappy quilts or usable yardage. It takes the worrying about how much out of the equation....buy what you can afford.
