4 Ways to Make Half Square Triangles + Half Square Triangle Chart

Learn how to make half square triangles 2 at-a-time, 4 at-a-time HSTs, or with the magic 8 method. This easy HST tutorial and half square triangle chart will show you how!

Half square triangles are one of the most basic quilt blocks and are very common in quilting patterns.

So many traditional quilt blocks are build upon half square triangles. And you almost can’t find a star quilt pattern that doesn’t use HSTs!

You’ll also find many modern patterns that make good use of them. Just look at our Mirror Maze pattern! It’s all HSTs and just so gorgeous!

As you’ll see they are really very versatile, so no wonder they are so popular!

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Table of Contents

1. What Is A Half Square Triangle In Quilting?
2. Making Half Square Triangles
3. Method 1: 2-at-a-time HST Method
   • Method 1 Cutting Dimensions
4. Method 2: 4-at-a-time Half Square Triangles
   • Method 2 Cutting Dimensions
5. Method 3: Magic 8 Half Square Triangles
   • Method 3 Cutting Dimensions
6. Method 4: Strip Piecing Half Square Triangles
   • What Size HSTs Can You Make From Precut Strings?
7. Half Square Triangle Chart

What Is A Half Square Triangle In Quilting?

A half square triangle block or HST in quilting is a basic patchwork block that consists of two 90-degrees triangles that together form a square. The triangles are sewn together along their long side (the diagonal).

What is HST in quilting terms? It’s simply an acronym for the ‘half square triangle’. These acronyms get used a lot in the quilting world, and I know it can be confusing at first. But now you know 🙂

Making Half Square Triangles

There are many different methods of making half square triangles and I’ll go through the four most popular in this article.

Choosing which method for half square triangles to use will depend mostly on how many HSTs you need for your project and also on your personal preferences. Each method has its pros and cons, so I suggest you try them all at one point to see which will work best for you.

Method 1: 2-at-a-time HST Method

If you only need a few half square triangles, or want them all in different fabric combos, this basic HST method is perfect. I use it sometimes when I’m trying out new layouts or to use up scraps of fabric from my stash.

Here’s how to make HST 2 at a time.

1. Place two squares right sides together. Draw a diagonal guideline from corner to corner.
   
2. Sew two seams, each a ¼’’ away from the guideline. 
   
3. Cut in half along the original guideline, open, and press seams out.
   
4. Trim your HSTs to the desired (unfinished!) size.

Method 1 Cutting Dimensions

We recommend making your basic blocks a tad oversized to accommodate for imprecise cutting and sewing. It happens to the best of us, so adding a bit of extra fabric to make sure you get the perfect size block is well worth it in our opinion.

The oversized formula for 2-at-a-time half square triangle is:

Starting square = Finished HST size + 1’’

You can use this formula to calculate the starting squares or – what’s even faster – use the half square triangle in Quilt Geek, our quilting calculator app:

Quilt Geek’s handy block calculators calculate the required starting pieces dimensions for different block construction methods.

Enter finished size, unfinished size or even one of the starting dimensions and Quilt Geek will return all the other numbers you need!

Learn more about Quilt Geek’s 20+ calculators and charts here or get started right away:

We’ve also created a handy half square triangle chart so yu’ll always have it on hand, make sure you get it (for free!) at the end of this article!

Method 2: 4-at-a-time Half Square Triangles

This method uses larger starting squares to make 4 HSTs at a time. 

The disadvantage of this method is the fact that it produces bias edges (the edges of the HSTs are on the bias grain of fabric). This can cause stretching of the edges and can distort your blocks. Make sure you carefully press your HSTs (and not iron them back and forth) to avoid distortion and you should be fine.

If you’re curious what these bias edges are all about, we have an in-depth article about the bias cut on the blog. Read our tips for working with bias edges here.

So how do you make 4 half square triangles at a time?

1. Place two squares right sides together. 
   
2. Sew a seam ¼’’ from the edge of the squares all the way around.
   
3. Cut on both diagonals. Open and press seams out.
   
4. Trim your HSTs to the desired (unfinished!) size.

Method 2 Cutting Dimensions

The formula for these quick 4 at a time HSTs is a bit more complicated as we’re dealing with diagonals here, so I won’t bore you with the math.

What’s much much easier is using our Quilt Geek’s half-square-triangle calculator and let it do the work for you!

The half-square triangle chart will also come in handy. It includes not only the cutting charts with the cutting dimensions but also illustrated diagrams to help you make your HSTs using any of the methods explained here. Get your chart here.

Method 3: Magic 8 Half Square Triangles

Yes, this method is so handy it’s almost like magic. Making 8 half square triangles at a time may seem complicated, but it’s actually not hard at all.

The great thing about this method is there are no bias edges to deal with. You’ll sew along the bias, which means the HST edges will all be straight grain. But despite this, make sure you handle the HSTs with care (and as little as possible) to avoid stretching and distortion.

Here’s how to make 8 HSTs at a time.

1. Place two squares right sides together. Draw two diagonal guidelines from corner to corner.
   
2. Sew two seams, each a ¼’’ away from each guideline (so four seams total). 
   
3. Cut the square into eights as shown on the diagram. You will cut in half vertically and horizontally and along both diagonal guidelines.
   
4. Open and press seams out.
   
5. Trim your HSTs to the desired (unfinished!) size.

Method 3 Cutting Dimensions

To figure out the dimensions for 8 at a time half square triangles, you’ll start out with the desired finished size of the HST.

The formula for 8-at-a-time half square triangle is calculated to reduce waste, which means it includes just enough fabric to make the 8 HSTs. Make sure you use a scant ¼’’ seam allowance, so you’ll have enough fabric to trim your HSTs to the desired size.

The oversized formula for 8-at-a-time half square triangle is:

Starting square = ( Finished HST size + 1’’ )  x 2

As I’ve mentioned before, you can also use the shortcut: our half square triangle calculator, which will calculate the starting squares for any desired HST size!

And another handy resource is our free HST cutting chart – get it here!

Method 4: Strip Piecing Half Square Triangles

Many quilters really like working with precut fabric as it often simplifies the cutting process. Let’s face it, cutting everything from yardage can be super tedious. In fact, the first few cuts, trying to handle the large pieces of fabric, are probably my least favorite part of making a quilt.

Luckily, there’s a trick to making half square triangles from a jelly roll, so if precuts are your thing, this will make you super happy.

So how do you make a half square triangle with a jelly roll? (Of course, this same method can be used for other precut strips of fabric, as well).

1. Place two fabric strips right sides together.
   
2. Sew a seam ¼’’ from both (long) edges of the strips.
   
3. Using a square quilting ruler and a rotary cutter, cut the triangles. Align the seam under the ruler with the mark for the desired unfinished HST size on the ruler. Cut away the fabric around the ruler.
   Example: The diagram shows how to cut a 2.5’’ unfinished HST. The seam is aligned with the 2.5’’ ruler markings.
   
4. Rotate the ruler to the other side of the strips and repeat the cutting process.
   
5. Open and press seams out.
   
6. Trim your HSTs to the desired (unfinished!) size.

What Size HSTs Can You Make From Precut Strings?

The formula for HST strip method is a bit complicated, as it deals with diagonals, and triangles and all those things you thought you’d never need to know again after high school.

I didn’t mind freshening up my geometry a bit to calculate what strip width you need for each (common) HST size. We’ve included it into our handy half square triangle chart, that you can get (for free) right here.

So if you’re wondering for example: What size HSTs can I make from a jelly roll?, you’ll look up the 2,5’’ strip width (because a jelly roll is 2,5’’ wide) and from there check the finished size of the HST you can get. The answer is – you can make 2’’ finished HSTs from a jelly roll.

The calculation will leave you a little bit of wiggle room for cutting, but make sure your seams are really  ¼’’ or a little bit less. If you make them too wide, the strip might end up being too narrow for the desired HST size. Also, keep in mind that the HST sizes listed in the chart are the largest you can make using the given strip width. You could always make them smaller with the same strip width, but you would have more waste.

Half Square Triangle Chart

Finally, the half square triangle chart! I feel like I’ve been talking about this thing nonstop in this article.

This handy half square triangle chart is the only HST cheat sheet you’ll ever need. 

It includes not only the HST cutting charts for four different methods but also illustrated diagrams to help you make your HSTs with the chosen method.

It’s a free gift for our newsletter subscribers, so if you want it, just fill out the form below and get it instantly in your inbox.

DTQ TIP: If you’re planning a whole quilt top, use the Fabric Yardage Calculator that calculates the yardage required for your project!

There you go. These are the four different methods to make half square triangles. All that’s left to do now is find a HST project and get practicing!

We’ve got a bunch of half-square triangle patterns you can try. For example, you can make our free modern herringbone pattern (super cute and it only uses HSTs) or make the mesmerizing Mirror Maze quilt!

If you’re feeling like you want to design something on your own, make sure you read our tutorial on how many blocks you need for your quilt. You can even add sashing (learn how to calculate sashing yardage here) and/or borders (learn how to calculate borders here).

Happy sewing!