How to Quilt: Master the Half-Square Triangle

What is a half square triangle? Only one of the most popular building blocks for patchwork quilting! If you know how to quilt with half triangle units, you will greatly expand your quilting repertoire.

The units, also known as HSTs or triangle squares, are simply two triangles that make up a square. You can make them large or small, use them here and there in a pattern, or create a whole quilt just with HSTs.

half square triangle quilt
Kona Cotton solids from Robert Kaufman Fabrics cut into half-square triangles make this Postcard from Sweden quilt burst with color.

Often, HSTs are made up of one solid color triangle and another of the same color but a lighter or darker value to create a shading effect, such as the quilt pictured here. But you can also use HST fabric combinations to create intricate designs on a quilt top, as border, as an accent, and hundreds of other ways.

There are a couple of popular techniques for making half square triangles. One is to cut two different squares into triangles and stitch the new square together on the bias.

With that method, however, you run the risk of stretching the fabric on the bias, causing the square to be, well, out of square.

The other method has you stitch first, then cut. Bonus: This method creates two HSTs at once. Read on for the directions.

To make a half-square triangle unit:

how to quilt half square triangle tutorial
Make 2 half square triangles at once.

1. Decide on the measurement of your finished squares in the piece you are making. Once you have that measurement, add 7/8″. For example, if the finished square = 2½”, the cut size of your fabric squares should be 3-3/8″.

(For the math challenged, you convert the 2½ to 2-4/8ths, add 7/8s, and that gives you 3-3/8ths.)

2. Cut your squares to this larger measurement.

3. Choose two squares you want to piece together to make a half-square triangle unit. Draw a diagonal line from corner to corner on the wrong side of the lighter of the two squares. (figure 1) Place the squares right sides together.

half square triangle tape
You can eliminate time drawing pencil lines on the fabric with HST Tiger Tape.

4. Sew a ¼” seam on each side of the marked line. Cut the fabric apart on the marked line to create two half-square triangle units. They should now measure your finished size.

5. Open and press to the dark side.

Making half-square triangles takes time, but once you’ve created all your squares, you can save time by string piecing or chain piecing them.

Other easy ways to make half-square triangles using quilting tools like HST Tiger Tape to mark the lines instead of drawing them or Thangles, strips of paper in various sizes that you pin to your fabric before sewing and cutting.

There are even techniques for cutting up to eight triangles at a time!

half square triangles courseWhatever method you choose, with all the notions, tools, and quilting tutorials available, if you haven’t made HSTs before, there’s nothing stopping you.

In fact, if you’re new to HSTs, Liz and Elizabeth Evans have a terrific online course that will help you get started.

With a little practice, knowing how to quilt with half-square triangles is a skill you’ll use again and again.

Happy Quilting!

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How To Quilt
Cate Prato

About Cate Prato

Cate Coulacos Prato loves fabric, thread, and dabbles in all types of fabric art. As Senior Online Editor for Keepsake Quilting, she welcomes your thoughts, ideas, suggestions, and discussion on quilts, quilting, fabric shopping, and the quilting community.

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