If the diagram Gay posted is correct, ignore my advice regarding resizing the units that will become half square triangles. This is why it’s so important to draw out the pattern.
For half square triangles, take the new finished size (3” & 1.5”) and add 7/8” for the cutting size. This makes 2 half square triangles at a time (though you could use your favorite method to make more (or less) at a time). A square 3 7/8” will make 2 3” finished at 3” and a square 2 3/8” will make 2 1.5” finished.