Originally Posted by Glassquilt
Tradition 9-patch each square is 4½" before sewing with ¼" seam leaving finished size of 4".
When you cut the center squares in half & resew with ¼" seam the strip has a finished size of 1¾"
With these dimensions the D9P block has a finished size of 11½".
12" is bigger than 11½" by 4%.
Instead of 4.5" you need to cut 4.674 (Sorry about switching between fractions & decimal)
4% of 4" is .174 which is approx 11/64 (greater than 1/8 but small than 3/16)
.174 plus .5 (½) seam allowance = .674 or 43/64".
Improvise. A whole lot easier than attempting to be this exact with quilting tools.
See!! We can't even all do the math the same for that size of block with the D9P!! We can all come up with the right size square to cut for a 12 inch finished 9P though!