The .5 is the seam allowance (.25 around each edge of the block) if you are just doubling the pattern, you would only double the first number. A 2.5 block doubled becomes a 4.5 block. A 4.5 block doubled, becomes an 8.5 block, doubling the 8.5 block becomes a 16.5 block and so on.
Note: I'm just showing the math to double a block.
Last edited by quiltsfor; 02-24-2023 at 03:23 AM.