Originally Posted by MTS
But you could easily make a 12.5" FINISHED block (13" unfinished), as that works well on a 5x5 grid.
Each piece would FINISH at 2.25".
So the squares would all be cut at 2.75".
For the HST's blocks, the 3.5" starting squares are still big enough to trim down to 2.75" UNFINISHED.
And you're good to go.
I think you meant to say that each piece would finish at 2.5", so the squares would be cut at 3". This would make a finished block of 12.5", unfinished at 13".
The real question is why do you want a 12" block in the first place? The answer to that might give a clue as to the best way to proceed.