By now you should be an expert on nine-patch blocks – dark and light arranged three across and three down. If you want to make your own, you can make them any size that you want. To do that, just figure out what size you want your finished block to be, and divide by three. Then add 1/2″ for the seam allowances and you are good to go.
This is really simple if you want blocks that are 6″, 9″, or even 15″ – those numbers all divide nice and evenly by 3. What if you want an 8″ block? Sure, you can divide by 3, but then you end up with math like 2-2/3″+1/2″. Even if you want to bother with the math to get 3-1/6, no quilting rulers come with 1/6″ lines. I have a trick I use to do this. It is what I used in the double nine patch block – find something close. Eight is 5 + 3, so it is also 2-1/2 + 2-1/2 + 3. You can make a block with 2-1/2″ squares on the corners and a 3″ square in the centre. The side pieces will be 2-1/2″x3″ rectangles.
I usually put the odd measurement in the centre so that all the pieces are squares, but there is no reason that you have to. You could have the centre and one corner at 3″ and one corner at 2″. That makes the other two corners 2″x3″.
Another interesting option, is to make blocks that are not squares. Here is a quilt I made for my daughter. The embroidery designs didn’t fit nicely into a square block, so I make the blocks 6″x9″ rectangles. (I chose that size deliberately because it was easy to divide by 3.)
I personally don’t like cutting to more than 1/4″ accuracy. Although I can do the math on paper, it is much more difficult in implementation. When you are designing, if the math is too hard, you have the power to change the question. Don’t you wish you could do that with every difficult thing?