The reason for the sizes are, your 4 1/2" patches only need to allow for one seam allowance of 1/4", your QST patches must allow for two 1/4" seam allowances across the diagonals of the block. The formula for QST's is Finished Block(4") Size+1 1/4". I usuall allow a bit more then square up, it's much easier and they fit better.