Originally Posted by k3n
The formula is:
(size of patch x 3) subtract 1 = unfinished size of nine patch, then subtract 1 (represents 4 x 1/4" seams) = unfinished size of new block if nine patch is cut into quarters and sewn back together.
Wouldn't you get the finished size if you subtract 1 again after cutting for the second sewing? For the unfinished block you only need to substract 1/2 inch, as there are only two seem allowances per block direction.