Originally Posted by susiequilt
Using 2 7/8" will result in 2 inch squares so it does include the seam allowance. I would recommend you use 3" squares and plan to trim the blocks to 2" when done. That 1/8" could make a difference in a block to small.
The math works. You always add 7/8" to what your FINISHED size will be. Since you need four half square triangles to make a pinwheel, each HST will measure 2 1/2". Once you sew all 4 together, you will end up with a 4 1/2" block, which will finish to a 4" block. At the same time, you could easily start out with a 3" square and trim each HST to 2 1/2", then sew 4 of them together.
Pinwheels are my favorite block. :lol: :D