If you need to end up with a finished 2 1/2 square then before sewing it would be 3". If you wanted a 2" finished square then you would cut at 2 7/8".

The term "finished" refers to the size of the HST after it is sewn into the quilt. The term "unfinished" refers to the size of the HST (or other block) before sewing into the quilt. It sounds like you are looking for a 2 1/2" unfinished HST which will finish at 2" after sewn into your quilt. If so, you will need to start with 2 7/8" squares to make the HST.

The terms can be a bit confusing since when you finish making your block, it comes out to an "unfinished" size until you put it in a quilt which takes the 1/4" seam allowance off on all four sides.

Hope this helps.

You gave a great simple explanation!! That's it in a nutshell!!

Often new quilters confuse finished size with block size. If I'm doing a 2 1/2" square I start with 3".

Lanny

I always add a full inch to the finished size I am looking too. 2&1/2 finished, use (2) 3&1/2 inch. It's easier to trim than to come up short, even a small amount matters in accurate piecing.

if you want them to finish at 2", be 2 1/2" as individuals you add the 7/8" to the 2"- not the 2 1/2" size (you add to the finished size- which would be 2"-not 2 1/2" the 2 1/2" is the unfinished size you want.
the way you did it is correct for making 2 1/2" finished blocks...unfinished 3" --- 1/2" seam allowance

Or you could use the Strip Tube ruler and method by Cozy Quilt. If you want more information, PM me.

Nothing you did it correct and they are correct. Now when you sew those together in the quilt they will be 2 1/2 half square triangles finnished size. You just did not use them yet in the quilt top. when you piece you will loose 1/4 inch on each side. So the 3 inch will go to 2 1/2 inch.