Lay out the block grid
Enter the finished size of one square block and the number of rows and columns. Use finished sizes throughout, rather than the larger unfinished blocks on your sewing table. Choose a finished width for the sashing between blocks. Seam allowance is added to the cut sizes for you.
Decide whether to use cornerstones
With cornerstones, the horizontal sashing is cut into short pieces between blocks, with a square at each inner intersection. Without cornerstones, those horizontal strips run continuously across the rows. The quilt dimensions stay the same, but the strip lengths and number of pieces change. The cut list follows the option you choose.
Add outer sashing separately
Outer sashing goes around the whole grid. Enter zero if you don't want it. When you add it, the plan uses continuous left and right strips first, followed by the top and bottom strips. Outer cornerstones aren't included. If you want them, plan those corner squares and shorter outer strips separately.
Check a three-by-four layout
Twelve 9-inch finished blocks arranged in three rows and four columns, with 2-inch inner sashing, make a 42 × 31-inch center. With inner cornerstones, you'll need six cornerstone squares. Adding 1-inch outer sashing increases the finished size to 44 × 33 inches. Check your block measurements before cutting the full batch.