Robert Kaufman's QuiltCalc for ipad gets 8.23 yards for backing. That is an 80 x 90 plus the 6 inch extra for shrinkage when quilted. Figure the top is the same - 16.5 yards. It sounds crazy to me but I've never made anything bigger than a lap quilt. Maybe someone else on the board can shed some light on this. Oh, I have a quilt pattern handy, 81.5 by 97.5 yep 13 yards for the top. 7/8 ths for binding and 6.5 yrds for backing. Now that happens to be for a pretty complex design which requires a wide variety of fabrics and shapes, so there would be more waste but even still. Other threads on the board have been discussing how surprised non-quilters are when told how much they are charging for their quilts. Well this quilter is surprised at the amount of fabric alone. Those selling bed size quilts probably aren't getting enough $ for them to make anything. You still have to quilt it and figure in some kind of payment for your time. Now I know why, many years ago I paid almost 1,000 for an Amish applique long queen. I bought it because I knew it was never anything I would make for myself. (and we had the $ at the time).