How to Make a Half Square Triangle Quilt Block

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A half square triangle or HST is one of the easiest and most versatile quilt blocks you can make. It can be rearranged into almost countless different designs to create a wide range of easy and unique quilts. Today I’m going to show you how to make a half square triangle and how to assemble these blocks into a larger and more complex quilt block.

What is a half square triangle?

A half square triangle (HST) is a basic building block that you can use on its own or with other HSTs to create complex designs in quilting. It is a simple construction made of two triangles, usually in contrasting colors so you can create designs.

The magical thing about half square triangles is that you don’t need to cut out a bunch of triangles and sew them together. Instead, you sew squares of fabric together and cut them apart in a particular way to create the triangle effect. We’ll cover that process in detail below.

Above you can see some HST quilt blocks I assembled with blue and red fabric from my stash.

I get almost all my quilting fabrics from Green Fairy Quilts. They have a great selection also some awesome sales. I usually find their regular prices are better than larger quilt fabric shops as well.

How to Make Half Square Triangles

You can make HSTs two at a time or four at a time. This post covers how to make HSTs with the four at a time method. This is my favorite technique not just because I find it easier, but because you get more squares at once. Here’s how you do four-at-a-time HSTs step by step:

Choose Contrasting Fabrics

For best results, you will want to choose fabric with at least some contrast when making half square triangles. If there is too little contrast, you won’t be able to see the final design. I personally like creating a subtle contrast by choosing fabrics with bold designs or unique colors because it creates a scrappy look. However, you can use any fabric you like.

If you want to use your HSTs to create a larger quilt block, think about the colors you will need to create a distinctive design. For this tutorial, I’m making an 8-point star quilt block*, so I’m using an equal number of light and dark fabrics.

You will need two pieces of fabric to make each set of HSTs. If you want to use the blocks to create a star design like me, you will need 8 squares of fabric.

* You can create star blocks using all half square triangles or by combining them with plain squares of fabric. For the 8-point star block I made, it would technically be easier to use plain fabric in the corners. However, I like the flexibility you get when using all half square triangles. You can change your mind about the exact layout after creating your HSTs. I’ll cover layouts more at the end of this post.

Cut Fabric into Squares

HST quilts are a great opportunity to use up charm packs and layer cakes if you have a lot of pre-cut fabrics lying around. I’m using charm packs to make my HST blocks.

If you don’t have pre-cut squares, you will need to cut your fabric into squares before taking the next step. I like 5″ squares but you can make any size you like.

Pair Fabrics & Pin

Next you will decide which fabrics you want to use for each HST. When doing the 4-at-a-time method, you will get 4 identical HSTs from each pair of squares you assemble.

To prepare the squares, lay two pieces right sides together (shown above) and clip or pin around the outside. I use these quilt clips and they work great for holding your pieces together.

Sew Squares Together

Now it’s time to start sewing! To make 4-at-a-time HSTs, you will sew a 1/4″ seam allowance around the entire border of the paired squares. The stitching will look like a frame around the entire square.

Cut Squares Apart

Next, you will use a rotary cutter to cut across your sewn squares at a 45 degree angle. You will make two diagonal cuts from corner to opposite corner – like making an X across the square. This will give you four identical pieces.

Press Seams

After cutting your squares apart, lay them open and press the seams to one side. I don’t personally worry too much about the direction I press the seams because it’s hard to know exactly how you will end up arranging your HSTs in the end. I usually just pick one color and press all my seams towards that side so each block has some consistency.

Square Up

The last step before using your blocks is to square up the corners. This will help you align your HSTs perfectly when using them for larger blocks. To square up, lay a cutting ruler over the block and use a rotary cutter to trim off any excess fabric that isn’t perfectly square.

I like using my 6.5″ square cutting ruler when squaring up my blocks because it’s easier to maneuver around the cutting mat.

Using Half Square Triangles

Now comes the fun part! You can use HST blocks to create an almost endless number of designs by arranging them in different ways. For the sake of this tutorial I’m going to show you how to make a basic star design.

As I mentioned above, you can use HSTs in combination with plain fabric and other blocks to create an even wider range of large blocks. I personally like the flexibility of using all HSTs because you can swap around the design and layout of your blocks so easily.

When using HSTs to create a larger quilt block, play around with the pieces until you get a design you like. ere is how I decided to arrange my star. Because I used 8 pieces of fabric in two contrasting colors, I do have colorful corners in my star design. If you prefer not to have this effect, you could use plain fabric in the corners instead.

Sewing the Pieces Together

Once you like the layout of your block, you can begin sewing. I find it’s easiest to make strips and then sew the strips together at the end. Below you can see the strips I assembled:

After making the strips, be sure to press them. If anything is out of alignment, you may wish to square up the strips after pressing. You can then pin them together and sew to complete the block as shown below:

Finally, you will want to square up your final block after pressing it. This will make it easier to use your block in a quilt later on.

Ready to do something with your quilt blocks? See how I used my blocks to create a gorgeous HST quilt top!