I think the formula for amount of binding needed is 2 X length of quilt plus 2 X width of quilt Plus 10 extra inches for the amount of binding it takes to square the corners and join at the end....I usually cut width of fabric and round up so sometimes I have almost 40 inches of binding left which I save in an "extra binding" box. sometimes I join these odd binding ends together to use on a scrap quilt, or for a smaller project or just iron them out flat again for 2.5 inch strips as I always cut my binding that size.