Kathie, you can but it won't be easy. The first block has 3 squares to make up the block. 20 inches divided by 3 is not an easy number to work with (6.66 inches). 18 inch block (6" squares) or 21 inch block (7" squares) would be easier to do. And you can get a 19 1/2 inch block with 6 1/2" squares. I'm not even going to guess on the second block because the squares within the block do not appear to be the same size.