Half Square Triangle Block Tutorial

Half square triangle red + aqua quilt
I’ve recently been amused by the half square triangle. This block is named as such as it is created from a square which is then cut in half on the diagonal. Two different triangles are then sewn to one another on the diagonal, which transforms them back into squares. Pretty simple.

The bias cut edge of woven goods that results from cutting fabric on the diagonal is somewhat vulnerable as the natural stretch of the bias cut is prone to fraying and stretching. Without proper care when handling, pressing and sewing, your work can quickly become distorted and subsequently be difficult to accurately piece. It is for this reason why many quilters use the following sure fire method for creating simple and accurate half square triangles without exposing the bias cut edge.

half square triangle template
The image above depicts a 5” square however you can use any size square that you prefer.

1. Select and cut
Select two different fabrics and cut each one into a 5” square. I prefer to use one light and one dark fabric.

2. Draw
Using a pencil, lightly draw a diagonal line from one corner to the other on the wrong side of one of your squares.

3. Assemble and pin
Assemble the two squares with right sides facing one another, making sure that the square on which you drew the diagonal line is facing up. Pin the squares together using one pin on each side of the diagonal line. Make sure to leave enough space for your your sewing machine foot to pass by the pins.

4. Sew
Sew a 1/4” seam on each side of the diagonal pencil line.

5. Cut
Cut your squares in half along the diagonal pencil line.

6. Press
Press flat then press the seam allowance to one side. I prefer to press toward the darker of the two sides.

Half square triangles pressed
7. Trim
Square up your blocks by trimming. When starting with a 5” square, blocks will trim to 4 1/2” x 4 1/2”.

Half square triangle fat quarter template
If you plan on making a number of half square triangles using the same two fabrics, you can mass assemble these. The image above depicts how to layout twelve, 5” squares using fat quarters. I like to draw the 5” squares first and then draw the diagonal lines. If you begin your sewing in one of the corners, you can sew on each side of the diagonal line continuously, without interruption. This arrangement yields 24, half square triangles fairly quickly.

Half square triangle arrangement 1
Half square triangle arrangement 2
Half square triangle arrangement 3
You can arrange your half square triangles into a number of shapes. Play with the lights and darks until you get the effect that you like.

Half square triangle babies
These little half square triangles were made using the 5” square method as described above however with a few extra steps added. I drew two, crossing diagonal lines through my square then sewed on both sides and cut accordingly. These pieces were then halved again using the same method. This resulted in these cute little babies.

It will be a little while before I have my two, current half square triangle projects assembled, batted, quilted and bound, but I’ll be sure to show you the final results when I am finished!

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