I buy a lot of coordinated fabrics. I buy 1/2 yard pieces for the main top (at least 6 different ones) then a couple of one or two yard pieces or borders. I like to make quilts to fit my queen beds, and they take pretty much fabric for the top. If you think about how big the backing is for a queen quilt (at least 7-1/2 yards) then you will need about that much for the top. That is how I figure it when I don't have specific instructions on how much to buy.