Here is a calculator for setting triangles and blocks:
https://files.allpeoplequilt.com/wp-...d_trianges.pdf To use this, take what your quilt block size is on the main top and use that measurement to find what you need for the other pieces.
i think this is the one the above poster is talking about.
https://quiltnotes.com/pages/107-OnPointCalculator.php
the calculator for this one:
https://quiltnotes.com/pages/106-OnP.../>
Results.php
I would forget about using 2 squares and two rectangles -- basically I would use the calculator to figure out what size block I need and then I would sew 4 smaller squares together with the fabric colors you need, to make that large size square, then I would cut that square in half diagonally. Make sure to leave the seam allowance at the point where the full square and the two triangles meet in your picture when you cut that oversize (4 squares together square) diagonally.