I've tried several methods for making half square triangles. Everything from special rulers, paper sheets, drawing grids and sewing strips but keep coming back to this quick sew method using easy to cut squares. With this method you can avoid dealing with the bias edges you'd be working with if you simply stitched two triangles together.
Cut squares from your two fabrics that are 7/8" larger than the finished size of the half square triangle units you want. For 3" finished size half square triangles you would cut your squares 3 7/8".
- I will admit to cutting my squares a full 1" larger than the finished size. After I've made the units I trim them to the exact size so they're all the same.
On the wrong side of one of the squares, draw a line diagonally from corner to corner.
Place fabrics right sides together.
Sew 1/4" away from the marked line on both sides.
Cut on the marked line.
Press the seam allowance to one side toward the darker fabric.
You'll get two half square triangles from each set of squares.
If you cut your squares larger like I usually do, line up the 45 degree angle line on a square ruler to trim them to size. Remember: if you cut 4" squares for 3" finished size half square triangles you'll be trimming the squares to measure 3 1/2" which includes your 1/4" seam allowance.