I'm having the same problem with figuring how much material I need to make a queen sized Rag Quilt, I think I might try to use Prisms idea, I have the 5 1/4 Go Rag Die.
OK oldtisme, after you subtract you 1/2" seam allowance on a Rag quilt, you are going to have 4.25" finished square. If you don't put a border on, queen in width is normally around 90" So you will need 22 squares across. The length is normally 108". Then you will need 26 in a row. 25x22 is 572 squares. That is a lot of squares and you need twice as many if you start to count the backing !! GOOD LUCK !!!