joe'smom, the system that I use was set up by a blogger - Carole, From my Carolina Home. She has stopped doing her monthly Stash Busters post but the formula she used was - you take the size of your quilt, say it's 80 X 80, multiply the size ( 80 X 80 becomes 6,400) now you divide that by 1,440, that number comes from the square inches of a 36 X 40 - the approx. size of a yard of fabric. Now you take those numbers say 6,400 and divide it by 1,400. Now you have a approximate yardage for your quilt top. So the 80 X 80 quilt top used about 4.44 yards. Hope this helps - sorry I know it's probably clear as mud.