Let say for convenience sake that I am stitching two square pieces of leather together. I am using a single stitching needle and going through the holes one way and then back the whole way and then tying the two threads together. A very basic stitch. But if I don't use enough thread the whole stitching process has to be done over. But I don't want to use too much thread either because then there is thread that is wasted. How do I know how much thread to use?