How To Make HSTs (Half Square Triangles)

Author: Meg Kelly



Time to read: 2 min

Are you new to quilting and wondering how to make an HST? Maybe you are wondering what an HST even is? HST stands for Half Square Triangle. An HST is a block made of 2 half square triangles, usually in contrasting fabrics that can then be used to make all sorts of designs and patterns. 

In this tutorial, we'll show you our favourite method for making HSTs, which is to make two HSTs at a time. We've also included a cheatsheet (see below) to help you decide what size to cut your starting pieces to ensure you end up with the finished block size that you desire.

Making HSTs Two At a Time


HST Half Square Triangle
WS Wrong Side
RS Right Side
RST Right Sides Together

With this method of making HSTs, we are making them two at a time. We'll make them slightly bigger so that we can trim them down to the correct size. As I've mentioned before, this is my favourite method to use when making Half Square Triangles. Starting with a bigger block and trimming it down to size, allows you to get perfect HSTs every time!

Cut as many squares as you will need finished HSTs. i.e if you need 10 finished HST blocks, you would cut 5 squares of your main fabric and 5 of an accent fabric.

Use the chart below to determine the size you'll need to cut your squares.

Half Square Triangle Cheat Sheet

Two at a Time Method

Finished HST Unfinished HST Starting Square (Cut 2 per block)
2 in. 2½ in. 3 in.
2½ in.
3 in. 3½ in.
3 in. 3½ in. 4 in.
3½ in. 4 in. 4½ in.
4 in. 4½ in. 5 in.
4½ in. 5 in. 5½ in.
5 in. 5½ in. 6 in.
5½ in. 6 in. 6½ in.
6 in. 6½ in. 7 in.
6½ in. 7 in. 7½ in.
7 in. 7½ in. 8 in.
Wrong Side Right Side Fabric Key

Sewing The HSTs

Take half of your squares and using a fabric marker, make a diagonal line from one corner to the next on the WS of the fabric. In this case, I have chosen to mark the back of the main fabric.

Place the marked square on your accent square RST. Pin squares together. Sew a seam a ¼ in. away from the centre line on either side.

Layer the marked fabric on top of the accent fabric RST
Sew 1/4 inch from either side of the marked line

Cut the sewn square in half down the centre to create two HSTs. See below image. Press seams open.

Cutting The Sewn HSTs
This is what you should have when finished cutting.

Trimming the HSTs

Place the 45° line on your ruler in between the two triangles. Trim a small amount off two sides.

Rotate the HST and trim the HST to the Unfinished Size. Refer back to the cheat sheet if necessary. In my example, I wanted my finished HST to be 2 in., so I trimmed my unfinished HST to 2½ in.

Trimming HST blocks made using the 2 at a time method
Trimming HST blocks

And now you have a completed HST block. You can make as many as you'd like and piece them together to make bigger projects like pillows or throws.

Half Square Triangle Quilt Blocks
HST blocks in an assortment of sizes

Come back next week and we’ll show you how to turn these HSTs into a throw pillow or toss cushion, depending on where in the world you’re from!

3 Quilt Patterns That Make Use of HSTs

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