Prarie,
If you stitch OVER ONE square on 14-count, the finished pattern size will come out to the same size if you stitched OVER TWO square on 28-count. Either way, you should make sure you add an extra 2 inches of fabric on EACH side of the fabric you order so you have enough fabric for mounting and framing your completed project. I add 3 inches on each side, but that's my choice....