I am making my first log cabin quilt. The finished squares will be 12x12. I want to buy a 12x12 ruler to square my blocks, but I can only find 12 1/2 x 12 1/2. I looked at LQS & online. Do they make a 12x12 ruler? Thanks, Maxine

they are 12.5 to allow for the 1/4" seam allowance...so when it is finished it will be 12" square.

I usually lay the block on my cutting mat at 0 (zero) and whatever size needed, which in your case is 12 inches, and use the square corner of the ruler to make sure it's square and trim off the excess. Be sure to press the block before you trim it square.

If you want your finished block to be 12 inches the 12 1/2 inch ruler is what you want, you need the extra for seam allowance, once sewed together they will be 12 inches.

That's right. Using a 12.5 square ruler will give you a finished square that is 12 inches

Remember the difference between BLOCK size and FINISHED size. If you want to finish at 12", you will need the 12.5 ruler to allow for 1/2" seams.

Don't you want the blocks to be 12 1/2" so that when sewed together become 12"??

It can get confusing, when blocks sizes are mentioned, we need to be aware of the terms finished sized or unfinished. Most blocks unfinished sizes will be 1/2" larger to accomodate for the 1/4" seam allowance on all sides of it. So you would want a ruler that allowance you to square up your block to 12 1/2" :D:D:D
If you measure these blocks when your quilt is done, they will measure 12".

I think this is what I have to do. The block size is 12" according to the pattern. It will be 11 3/4" after the blocks are joined. This seemed odd to me, but it's the first Log Cabin I've done. I thought I'd be able to easily find a 12" square ruler to lay on top of the finished block-centering the "center" red square and trimming the edges.

It seems to me that your block size finished will be 11 1/2, not 11 3/4. Right?