Making Half Square Triangles

My last several quilts have involved making lots of half-square triangle blocks–lots and lots of them! The illustration above  indicates measurements for a finished block size of 6 inches (6 1/2 unfinished). The traditional method is to cut a 6 7/8 inch square in half diagonally from 2 different fabrics and then sew the triangles together along the long bias edge…tricky process to sew without stretching or getting the points tangled in the sewing machine when starting. There is a much easier way to accomplish the same thing. With a pencil, on the wrong side of one of the fabric squares, draw the cutting line from corner to corner. Then sew a 1/4-inch seam on each side of the line. Once sewn, cut along the marked line. Voila, 2 blocks.  Already it’s a much easier process.

But what if you have oodles of these babies to make, it’s still a lot of marking before sewing. What if two marked lines could result in 8 half square triangle blocks?

Hmmm…that looks doesn’t look like it would work….but wait. By adding two extra cutting lines, you’ve now got 8 half square triangles from 2 squares of fabric.

How do you calculate the size of this new larger square? Double the size of the original square needed. Here’s a tip that really helps me. To figure out the size of square needed for a finished size of HST block, I add 1 inch. If my finished size is 6 inches, then I need 7 inch squares to make 2 HST blocks. To make 8 blocks, I double that to 14-inch squares. If the moon and stars align, I should be trimming off that extra 1/8 when I square up each block using Quilt In A Day Triangle Square Up Ruler 9 1/2 inch…one of the best rulers in my inventory!

In summary:

Finished block Size plus 1 inch equals square size needed of 2 fabrics to make 2 half-square triangle blocks

Finished block size plus 1 inch times 2 equals square size needed of 2 fabrics to make 8 half-square triangle blocks.