Quilting How-To: Half Square Triangle Two at a Time Method

The half square triangle is a building block for many more complex blocks.  It can also be used in borders and by itself to make many amazing designs.

One of my favorite way to make half square triangles makes two at a time.

  • Cut 1 square of fabric for each of the two colors used in the half square triangle.  One purple and one white in this example.
  • Determine the minimum size of the squares by taking your desired finished square size and adding 7/8 inches to it.  For example if you want a 6 inch finished square then cut 1 purple and 1 white square of at least 6 7/8 inches. 

  • Cutting your squares a little larger than necessary makes everything easier and allows you to be more accurate.  For a 6 inch finished square I usually cut my starting squares 7 inches instead of 6 7/8.

  • Stack the two square right sides together

  • Mark diagonal and sew a scant 1/4 inch seam on both sides of marked line.  If you make your squares oversized you have to be less worried about the "scantness" of your 1/4 inch seam.

  • Cut on marked line to create 2 half square triangles.  Press seam toward the darker fabric or press the seam open.

  • Square up the patches to the finished size plus 1/2. For example for a 6 inch finished square trim to 6 1/2 inches.

  • To square up the block, use a ruler with a 45 degree line. Align the 45 degree line with the diagonal seam on the block.

  • Trim the edges to the proper size.

  • If you made the starting squares a little oversized, there will be more waste at this point.  However, there is less chance that the half square triangle will be too small!

Other tips and approaches:

  • Looking for a faster approach when you have many half square triangles to make using the same fabrics?  Try Thangles  papers.  They are available at most quilt shops or on-line.
  • Hate the marking part of these instructions?  Try The Angler 2 tool by Pam Bono.  It takes a few minutes to put it on your machine but allows you to skip the marking the diagonal part of these instructions.  This tool is great if you are making many half square triangles. 
  • Instead of marking the diagonal, lightly press (or finger press) a diagonal fold on the top square as your line to follow.