I try to have a general purpose in mind. Questions I ask myself: Would I use it for borders and maybe focus fabric, then get 3 yards. Would it be a background fabric, then 2 yards. A supporting fabric, then 1 to 1 1/2 yards. Would it make a good backing, then 5 or 6 yards ( or more depending on size of quilt). If you like scrap quilts then Fat Quarters are great.