I measure both ends and sides. Length and width twice. Set those figures aside. Then the top, middle, and bottom. I compare. I go with the longest and add a foot. My binding is always 2-2 1/2". I always check the edge of the quilt so I don't cover any part of the edge up. Twin size is not small length binding. I do between 3/8" and 1/2" seam allowance. there are videos to show measuring binding. Everyone has their own way of doing it but I still add extra. Not fun coming up short on the binding!