If all your pieced squares are about the same size (someone else said about the same thing) - measure them and cut your your solid blocks to that size.
I think you can "get by" if all your seams are the same size.
Mary Ellen Hopkins said something about a "personal measurement" in one of her books. :-)
Quick test for sewing - take three 2 1/2 inch strips, (they only need to be about four or five inches long) - sew them together, press them, and then measure them. The sewed strip should measure 6 1/2 inches across. If not, make adjustments.