Using corner stones makes the math easy and simple, you determine the width of your sashing and make each side the same size as the block. The corner stone/square is square so you just cut that size and add to one piece of the sashing.
So in my last sashed quilts the blocks were what I think of as non-standard sizes. The block finished to 7" (so, 7.5" raw). Although I wanted to have a finished 2" size sashing, I didn't have enough fabric for that but I had plenty to make a 1.5" finished (2" cut) width.
Getting used to designing your own projects can be a little confusing, some of us think better using the rough cuts and others think of the desired finished size + .5" seam allowance. And thank goodness for programs like Electric Quilt but you can do it all by hand and a pad of graph paper.
But basically, you cut the length you need by the width of your sashing. So for a 7" finished block, that meant my rough size for that side was 7.5". My sashing finished at 1.5". Adding that measurement meant I was basically making an 8.5" finished square, so that meant my longer side was cut at 9" inches (8.5" finished + .5" seam).
If you used corner stones, no math needed, just two pieces 7.5 x 2", plus one square 2". Most people use contrast for corner stones, I try to eliminate excess seams if I can but you could be a glutton for punishment and piece in the corners all out of one fabric should you choose.
When I use corner stones, I do it as a strip piecing method and I still put them on like an L. I cut WoF (width of fabric) the size of the sashing, and the same for the size of corner stones and do a race on my sewing machine to see how fast I can get through it... I press and then I cut the unit at one time the desired width. You get much more consistent results and a much better use of time doing it that way instead of cutting a bunch of tiny little squares and putting them on narrow little rectangles. In my opinion any way! The point is there are many ways to do things and we have to figure out the best way for us to do them.
Last edited by Iceblossom; 11-09-2019 at 08:34 AM.