In the A box enter the size of your block.
In the B box enter 100 -- because your block is 100% at the size it currently is.
Then in the C box, enter the size you want your block to be, either larger or smaller.
Place an X in the D block and hit the calculate button.
The x will be replaced with the percentage you will need to either enlarge or reduce your pattern.

Example: Let's enlarge a 6" block to a 12" block. The first image shows all
the figures in the appropriate boxes. Note we have X in box D before we
calculate for the correct percentage.
The second image shows what happens after you hit the calculate button. The
X has turned into 200 and that is the percentage you will need to enlarge
your 6 inch block to turn it into a 12 inch block.

Before                                                                         After