I made a quilt with 10" finished HST's -- I used the 12.5" ruler to cut 11.5" blocks and trimmed (you get 2 blocks cut by most WOF, though I did go down to 11" cut on a couple of narrower fabric ad used a bit of the selvage). The beauty of 10" finished blocks is the arithmetic is easy (twin size 60x80 = 6x8=48 blocks, then add the borders). It was a lot of fun...