The web-site mentions 10" pre-cuts, and rulers of 8 1/2 and 4 1/2", so I assume the center block will finish at 4". If you don't want any more rulers, one could place a 4" square of clear/tinted adhesive dead center of the 8 1/2" ruler, which will easily square up the block to 8 1/2". Seems like a stack n whack - easy done.