Inspiring Quilters, Stitch by Stitch
I hate to say this but, I use math. Your base number is always 40 inches in width. Divide 40 by the size of the squares you need to cut. We'll just go with 4 inches. You can get 10 4 inch squares out of 40 inches in width. My pattern calls for 40 squares. That means I'll need 4 4 inch strips. That's 16 inches so half a yard will do.