Making Half-Square Triangles

You may see them called triangle squares or half-square triangles or simply abbreviated HSTs. They are found in many traditional pieced quilt blocks . . . so it's worth the effort to be comfortable with the math and the technique.

To make a pair of HSTs, you start with 2 squares of fabric, each cut 7/8 inch larger than the finished size you want. For the 6 inch Shoo-Fly blocks, the HST units in the corners finish at 2 inches, so you add 7/8 and cut your squares at 2-7/8. Some quilters round up and cut squares 1 inch larger and trim afterward. After the HST unit is complete, it should be 1/2 inch larger than the finished size (2-1/2 inch for our Shoo-Fly blocks).

Kate put together these great step-by-step photos and notes on one method for sewing perfect half-square triangle units every time.

1. First draw a diagonal line across the back of the 2-7/8 inch light (WOW) square. Then, placing the square right sides together with a dark (floral) square of the same size, stitch 1/4" away from the diagonal on each side.
   
   
   
   
2. Then cut the two halves apart down the original marked line.
   
   
   
   
3. Press open to yield two half-square-triangle (HST) units. For the March Shoo-Fly blocks, you'll repeat this with the other pair of 2-7/8 inch squares to make four half-square triangles (HST) units in total.
   
   
   
   
4. Check to make sure your sewn units measure 2-1/2 inches. Square them up as necessary at this stage.