How to Make Two Quarter-Square Triangles

Cut two squares of fabric 1 ¼” larger than the finished size. For example, if you need 3” half-square triangles, cut your squares 4 ¼”. Draw a diagonal line through one square. Stack on top of other square, right sides together. I first pin the outside corners together. Then I pin the other two corners. When sewing a bias (or diagonal) most directions will tell you to be careful to not stretch the bias. But when you sew ¼” on both sides of the drawn line, what really happens, is that the stitch draws the fabric up and shortens the stitching line. A “not to square” square results when you cut the square apart on the drawn line.
If I find that that is happening (it happens a lot with very fine fabrics), I will use a piece of cheap tissue paper as a stabilizer under the fabric at the stitching line. Just sew right through it. It tears off easily. Cut apart on the drawn line and you will have two half-square triangles. Press to one side.
Place one half–square triangle on top of other one, right sides together, with fabrics on top of opposite colors. Draw a diagonal line crossing the previous stitching line. Stitch ¼” on both sides of drawn line. Cut apart on drawn line. Press seam to one side.