I add up the length and width of the quilt to get the total length of the binding. 40 inches is always your base width of fabric number. So divide the total length (length+length+width+width=total length) by 40 and your answer is how many strips you need. If you get something like 6.3 you should just cut 7 strips. If you get an answer like 6.8 you may need a little more than 7 strips.