I have numerous stash building criteria. If I absolutely love the fabric and can't live without it I buy a minimum of 4 yards. If the sale is can't pass up good and the color is a neutral or a blender I will buy up to 8 yards, especially if it is a light neutral like cream or light tan, can always use it as a background color. Additionally if I find a really awesome sale like $3 per yard or less I will buy 8 yards as that is usually ample yardage for backing one queen size quilt or a couple of smaller quilts. I don't always coordinate my backing to the front. If I am shopping a batik sale I will buy in 2 or 1 yard chunks depending on color. If I am not familiar with the manufacturer or the fabric is of unknown quality I will buy smaller pieces as well. If I only spent $3 per yard and received a yard of not so nice fabric it isn't so bad.