Originally Posted by cjsews

Look on quiltville.com. Bonnie Hunter has a chart with dimensions to cut setting triangles

Originally Posted by PaperPrincess

Bonnie Hunter has great info on setting triangles. She provides the math and a chart:
https://quiltville.com/onpointmath.shtml

Originally Posted by Krisb

So...what is going wrong? The blocks in the runner may not be coming out at 6.5” unfinished. Did you square them up before you put them together?

Those pesky double diagonal cuts can be harder than they seem. If you measure one of the short sides, it should be a tiny bit over 6 7/8”. The dog ears extend past the edge of the block to which you are attaching the triangle, and your seam, if perfect which mine never are, intersects right at the raw edge.

Mine never do. I just start with slightly bigger triangles, like 10”, slice them twice diagonally, attach them, and trim the edge to make sure there is a 1/4” seam allowance past the points.

The four corner triangles are cut from 5 1/8” triangles sliced once diagonally; I would probably use 5 1/4”. Again, you can always trim later.