Sandra Lee Design

How to Make Half Square Triangle Units

Sandra Johnson

Half square triangle units are squares made up of two 90-degree triangles. Each triangle occupies half of the square’s space.

Two triangles together create a unit, and we are going to assemble the patchwork with quick piecing techniques that eliminate the need to handle individual tringles with stretchy bias edges.

What you will need

• Pencil
• Scissors
• Square rotary ruler and cutter
• Straight 
• Iron and ironing board

Materials

• Various fabric scraps

Instructions

            Cut and Mark Squares for Triangle Square Units

Refer to the pattern for the size of triangle square size and number of units required.

With your pencil or permanent marker to draw a diagonal line from one corner to the other opposite corner on the reverse side of the square.

Draw two more lines, each one ¼’ from the original diagonal line.

 Sew Squares and Cut Apart the Half Square Triangle Units

Let’s start with a pair of marked squares, edges matched and right sides together.            

Pin the fabrics and sew two seams, each ¼” from the marked centerline. Press to set the seam.

Cut through both layers of the square on the marked center diagonal.

            Pressing the Square Triangle Units

                        Press the half square triangles with the seams open.

            Making Oversize Triangle Squares and Trim Back

                        You can start with a larger square triangle piece of fabrics.

Once you have cut and pressed the squares you can trim the half-square triangles to the size you desire. I use a ruler “Slotted Trimmers”