If you are making hallf square triangles you need to cut your initial block 7/8" bigger than the FINISHED size of the block. If you are make quarter square triangles you need to cut your initial block 1 1/4" bigger than the FINISHED size of the block. So, if the finished block of 2 HSTs is 6 inches you would need to cut each of your initial blocks at 6 7/8 inches square. I cut a LOT of blocks wrong before I got the "finished" idea through my head. Good luck.