hi wolf -
sorry i am a dimwit today.
that should read - add 7/8 to finished size - or 1" to finished size (for cutdown method)
so -
12 1/2 unfinished - translates to 12" finished
12 7/8 for precision cutting and sewing -- or
13 for cutdown.
the grid part of my first post is correct
sorry again - nothing like someone helping you with bad info.
lefty in philly