bearisgray

I resort to graph paper.

I draw the "finished size" of the square and triangle on graph paper - then add seam allowances to my drawings.

Then I measure my drawings - I would probably cut them out and glue them to template plastic.

One can cut the triangles one at a time, as half-square triangles, or as quarter-square triangles. "How" one cuts the triangles is determined by the fabric available, and how you want the grain lines on the finished item.


For the drawing on the bottom - and you want to cut the triangles as QSTs from a square -

The (theoretical) formula is:

Center square: finished size plus 1/2 inch

Square to cut QSTs from: finished size of side of center square plus 1-1/4 inches (I would cut them at least 1-3/8 inches)

Example: Center square finishes at 4 inches - cut square 4-1/2 inches
Triangles - cut square 5-1/4 inches to cut into QSTs (I would cut my square at least 5-3/8 inches and trim.)