It depends on the fabric and how I plan to use the fabric. I agree with Tartan, if the fabric would be a focal part of the quilt. Sometimes you know it will make a perfect backing, then I buy the size of an average quilt for me, usually 5 - 6 yards. The next thing I look at is how the pattern repeats. I do not buy fat quarters because they never seem to be enough, so I buy a minimum of 1 yard because I know that I can make a rail fence quilt with 4 - 1 yard pieces of fabric to make a nice size throw. So try and determine what type of quilts you like to make and what size fabric do you need for those quilts.