How to Sew Half-Square Triangles (Method 4 of 6)

The half-square triangle is a basic piece used in many quilt blocks. Very simply, it is a square that is cut in half from corner to corner (diagonally) to create two triangles within one patch.

As amazing as it sounds, there are several ways to sew these units together. Some of these methods increase the accuracy of the resulting patch (for example Methods 2 and 4). Other methods increase the speed or convenience of sewing many half-square triangles (Methods 5 and 6).

Which method you use depends upon personal preference.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

• Sewing Machine or Needle
• Thread
• Fabric
• Scissors or Rotary Cutter
• Ruler
• Fabric Marker

1. 

   In this method, you will sew a triangle onto a square and the result will be one half-square triangle. I generally do not trim the side of the square that is under the triangle, but use it as a guide for sewing the half-square triangle onto other patches.
   
   Cut one square of fabric that is the finished size of your patch plus your 1/4 inch seam allowance.

2. 

   Cut one triangle for each square. It is easiest to use or make a template that is the square and triangle including the seam allowances. Mark your fabric (on the wrong side) around the template, then cut. Or place the template on your fabric and cut around the template using a rotary cutter.
   
   Generally it is best to place the square sides of the triangle on the straight and cross grain of the fabric, leaving the long side of the triangle for the bias. (The bias side stretches, and when you sew these triangles together, the bias will be sewn together and be stabilized.)

3. 

   Lay the triangle on top of the square, right sides of the fabric facing together. Match the corner of the square with the corner of the triangle.The bias of your triangle will run diagonally across the center of your square.
   
   Note that the triangle will take up more than half of the square. This is because of the seam allowance.

4. 

   Sew the triangle onto the square using a 1/4 inch seam allowance. Your stitching will go from one corner of the square across to the diagonal corner.

5. 

   Fold the triangle open so the right side is showing, and you have a completed half-square triangle.

Resources

• How To Quilt
• Quilt Block Library