Just Jan

I purchased Fons and Porter's "Easy Diagonal Sets" ruler. Its one of my favorite rulers. You do not cut squares you cut strips of fabric and cut your triangles by lining up the ruler on the strip. The markings tell you what width strip to cut for whatever the size of your finished block is. There is not math to do and you do not need to worry about straight or bias of fabric because all that is 'automatically built into the ruler'. One end of the ruler is for the side triangles and the other end is for the corner triangles. Works for from 3" to 12" finished size blocks. (I also like the easy to read yellow markings.) Its a real no brainer ruler and I highly recommend it.
*** Fran, I notice you said the blocks finished at a certain size. When I said the ruler gives the size for the finished blocks I mean the final size they will be when sewn into the finished quilt. So for example if your block currently measures 5 1/2 your finished block size would be 5". That's the size you look for on the ruler. If your block ends in a 3/4" you would round it up to the next full inch then deduct the half inch seam allowance to get the finished size of the block to choose. This ruler gives a generous amount to the triangles you cut so they will be over-sized when sewn in, allowing you to square up the quilt without cutting into your seam allowances. I hope this makes sense. Feel free to PM me if you want.