Half Square Triangles

QuiltNotes Learning Center

Last Updated March 23, 2019

half square triangle units The half square triangle (HST) unit is often one of the first units new quiltmakers attempt. If you take a square and cut it in half diagonally, two triangles make up the square. Or, another way to look at it,  there’s a triangle in half of the square.

Most often, the two fabrics used to make a half square triangle  contrast with each other. Depending on the way the unit is positioned, the design possibilities are almost endless. This is why you see HST units all over the quilting world.

There are many ways to construct the HST including using templates, rulers and grids. In this article we look at the grid method. Some grids can be drawn on the fabric and some grids are printed on paper. For these examples you will need two fabrics that contrast well with each other.

Make One Half Square Triangle

This method is the simplest way but not often the most easy to cut or accurate to piece. You simply cut a triangle from each fabric. Use strips of fabric to cut the triangles.

Cut Size

Determine what size to cut the strip. Add 7/8″ or .875″ to the finished size you want. For a 2″ finished unit, cut a 2.875″ strip. Download the reference chart, Half Square Triangles from Squares. If you think you might have problems with cutting and/or sewing accuracy, cut the strip larger and trim the unit later. In this example we want a 2″ finished HST unit and we will cut the fabric larger.

Cut a strip 3″ x WOF from each fabric. The grainlines will end up along the outside edges of the unit. For more information about grainlines read the article, Using Grainlines in Quilting

half square triangles

Place the fabrics right sides together and trim the left end straight.

half square triangles

Place the 45° line of the ruler along the bottom edge of the fabric strip. Align it so the ruler intersects the top of the fabric strip. This point is shown here with the purple pointer.

Half square triangles

Cut the strip along the ruler.

half square triangles

Using a 1/4″ seam, stitch the two fabrics together along the cut side. Press to the dark fabric.

Trim to Size

half square triangles

Trim the unit down to 2-1/2″. Use the 45° line on the ruler or use a square-up template or ruler.

half square triangles

Trim off the little triangle nubs, they just get in the way later.

half square triangles

Now you have a 2-1/2″ unfinished half square triangle. The finished size is 2″.

If we go back to the strips we started with, we see something interesting.

half square triangles

There’s another half square triangle unit there waiting to be stitched and trimmed.

Two At A Time

What if we made two at a time?

half square triangles

Instead of cutting off a triangle then cutting off another triangle, just cut a square.

half square triangles

On the light fabric, draw a line along one diagonal.

half square triangles

Stitch 1/4″ along each side of the drawn line.

half square triangles

Cut along the drawn line.

half square triangles

Press toward the dark fabric, trim off nubs and trim the blocks.

Next Make Four

Hang in there for a minute and you’ll see how it gets much easier because we use a grid.

half square triangles

Cut a 6″ x 3″ rectangle because this rectangle is just two 3″ squares put together.

half square triangle

Next, mark some lines. Mark a vertical line in the center. This defines the two squares. Next, mark one diagonal line in each square. These diagonal lines should touch each other as shown.

half square triangles

Once the lines are drawn, sew on either side of the diagonal lines. You always stitch adjacent to the diagonal lines, never the vertical lines or later, the horizontal lines.

half square triangles

Finally, slice the vertical and diagonal lines into four half square triangles.  Press and trim and you’re done.

Make it Easier

As you can see, making pairs of half square triangles starts with squares. If you need more than about six or eight half square triangles from the same fabrics, you can use the grid process just demonstrated. But drawing multiple lines on larger grids takes time. This is where triangle papers come in handy.

Because the products described below are paper foundations, you can quickly and accurately make dozens of half square triangles at a time. The products use paper and are very accurate. With all these methods it might be helpful if you used fabric starch to give a little stiffness to the fabric. This makes it easier to stitch and to achieve greater accuracy. See Using Fabric Starch in Quilting.



Thangles are a set of paper strips with grids printed on them. Place two strips of fabric together as shown in the pictures above. Place the Thangles paper strip on top. Pin the papers to the strip set and sew on the dotted lines. Slice on the solid lines.

Thangles are available in sizes from 1/2″ finished to 6″ finished and can be found at most quilt shops and online. There are also Thangles for making quarter square triangles. I have used Thangles when I don’t need a lot of HST. I prefer the larger grid when making stacks of HST. This is a personal preference and many quilters love the simplicity of cutting strips and piecing HST. Thangles are easy to use and you’ll should get accurate units with little fuss.



triangles on a roll

Triangles on a Roll

Triangles on a roll is a long roll of gridded paper. The half square triangles are available in eleven different sizes from 1″ finished to 6″ finished. One roll makes 1200 of the 1″ size. The 6″ finished size roll makes 176.

For a tutorial on how to use Triangles On A Roll check out How To Use Triangles On A Roll.

cake mix recipiesCake Mix Recipes®

Made by Moda, a Cake Mix Recipe® is a pad of paper grids for making half square triangles from pre-cut Layer Cakes®. Layer Cakes are 10″ squares of fabric. There are 8 different sizes for Cake Mix Recipes®.  Also available are Cupcake Mix Recipes® that use 5″ charm squares. There are 4 different sizes for those.

I received a package of these as a retreat gift but have not had a chance to use them. The grid is well marked. Since it is made for pre-cuts, you can get right down to sewing on the lines. One of my friends used Cake Mix Recipes and was very pleased with the results and the ease of use.

triangulationsTriangulations 4.0

This is a DVD containing PDF files you print with a printer. It is designed by Brenda Henning from Bear Paw Productions. A page contains the grid used for piecing. There are multiple pages for half square triangles, quarter square triangles and flying geese units.  The half square triangle foundations are available in sizes up to 7-1/2″ in 1/16″ increments.

I have used this program just once. Because all printers are different, you should know how to adjust the print settings for the PDF files. Complete Instructions are included on the DVD.

For more project tutorials and videos:

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