I have a quilting calculator which I got at Joanns. When they were half price at Joanns I splurged and bought 2. One for my sewing room and one for my purse. This gadget will figure out exactly what you need when you put in the quilt dimensions. It also factors in seam allowance and enough to leave at the top and bottom to allow for drawing up when quilting. With the price of fabric these days, I don't want to buy any extra. Depending on how wide the quilt is, you will probably have enough of the backing sides to use for binding.