2 critical tips to perfect Quarter Square Triangles

I remember my first project with half square triangles. I sewed the squares together on the diagonal, cut them in half, pressed and then trimmed. What did I know about trimming and using the diagonal line as a reference? Nope – I just laid the ruler on my half square triangle and cut out the size I needed! There wasn’t a SINGLE point on that quilt. I’ve since learned how to trim half square triangles and it’s now one of my favorite units.

The quarter square triangle used to give me grief until recently. Yes, I’m still learning; the day I stop – I’ll be dead!!!! And yes – I still get frustrated and I still make mistakes, but I’m enjoying the learning process. If everything I sewed was perfect, that means I’m not challenging myself.

So – I would make quarter square triangles and they would be wonky. Why? I spent some time one afternoon evaluating the problem and I found the solution which I’ll share with you today.

I’ll be using the Husqvarna Viking Designer EPIC to show you how to make perfect quarter square triangles.

Husqvarna Viking Designer EPIC

Tutorial for Quarter Square Triangles

There are different methods for making quarter square triangles. This tutorial uses half square triangles. As I work through the process, I’ll identify the pitfalls so you too can have perfect quarter square triangles.

The first thing is to cut squares. Just how big should those squares be? Start by determining the FINISHED size of the units you need. Let’s say you need 3½ʺ finished quarter square triangles, then add 1¼ʺ to the FINISHED size. That means you will cut squares that measure 4¾ʺ.

When you sew the quarter square triangles with this method, you’ll get two identical quarter square triangles.

Start by cutting two identical sized squares. They should have contrast to each other either in value or color. I happened to have some 5″ squares handy so I used those.

Two squares will yield two quarter square triangles

Draw a diagonal line on the wrong side of one of the squares. Place the two squares right sides together and stitch a scant ¼ʺ on both sides of the diagonal line. Try to keep those stitching lines as straight as possible.

Draw a diagonal line and stitch a scant ¼ʺ on either side.

Cut on the diagonal drawn line. Technically it doesn’t matter which way you press the seams, but be consistent. If you press one seam to the dark, then press both to the dark. If you press one seam to the light, then press both to the light. You should now have two half square triangles. DO NOT TRIM.

Two half square triangles

A potential pitfall is that the seams of the half square triangles are not pressed well. My seams are nice and flat. Always press these units from the RIGHT side. Never the wrong side. Why? You want to ensure that there are no tucks or folds in those seam lines, in particular at the corners. You can control that from the front, but you can’t see those potential tucks if you press from the back.

Another pitfall – be careful that you don’t stretch the seams.

In the photo below, the arrows are pointing to the corners – this area is usually not pressed well and can cause issue with your points in the final units.

Again, straight seams will give you a nicer finished unit.

Press well right to the end of the seam.

Now we’re going to draw another diagonal line on the reverse of ONE of the units.

Draw another diagonal line

WAIT – don’t just lay the ruler on and draw a line and don’t line the ruler up with the corners of that block. NO – you want to place the ruler so it’s more or less lined up with the corners, but more importantly, the line you are about to draw should be 90 degrees to the first seam line. This is critical to the success of your quarter square triangles.

Second line MUST be 90 degrees to the first seam

Place the two half square triangle units right sides together alternating the colors. So the pink is on the blue and the blue is on the pink as shown below. Nest those two center seams up to each other. If you recall from yesterday’s post, I would not consider pinning these units. They’re small enough that they won’t distort or shift. But very important that those two seams be nested to each other. That’s why it’s important that the seams be pressed to the same fabric. In this case, the seams were pressed to the blue fabric and this allows the seams allowances to nest against each other. This in turn helps to get a perfect intersection in the middle of the unit.

Place the two half square triangles right sides together

Carefully stitch a scant ¼ʺ on both sides of that new diagonal line. Notice that I haven’t used pins. Again, the straighter these lines of stitching are, the better results you’ll have with your quarter square triangles.

Stitch a scant ¼ʺ on both sides of the diagonal line

A scant ¼ʺ stitched on both sides of the diagonal line

If you want to check how accurate your centers are before you cut the units apart, pull back one of the loose corners. A perfect match – no pins!

Pull back the corner to check the intersection

Cut the units apart on the diagonal line.

Units are cut apart on the diagonal line

Press the seams. Confession time again – I did twirl those seams on the back. As I mentioned yesterday, old habits die hard. Plus I really like the look of the seam being distributed in all four directions, rather than have that final seam across the center of the block.

Twirled seams on the back

Two untrimmed quarter square triangles

The last step is to trim the units. It’s a whole lot easier, if you use a SQUARE ruler to do your squaring up. I’m right handed, so I position the ruler with the 1″ and 1″ markings in the top right hand corner. If I were left handed, those markings would be in the top left hand corner.

I now need to know the UNFINISHED size of my quarter square units. I want units that are 3½ʺ FINISHED so to get the unfinished size, I now add ½ʺ for the seam allowances. That means,  I’m going to trim these units down to 4″ UNFINISHED.

Preparing to square up the quarter square triangle unit

Like the half square triangle, there’s a better way to trim these units, which in itself becomes a critical step in making the perfect quarter square triangles.

In the photo below, you can see that I have 5 reference points. Since I’m trimming my blocks to 4″, I can use the intersection of the 2″ lines on the ruler to find the center of the block. Then I can place the intersection of the 4″ on the bottom left of the block. You can see the other three reference points below.

Now it may be not be exactly perfect, so you may have to jiggle the ruler around or you may have to jiggle your block underneath the ruler. Once it’s lined up to the best of your ability – then trim along the right hand side and the top side of the ruler.

Rotate the block 180 degrees. Line up the clean cut edges with the 4″ (in this instance) lines on the ruler and again, trim along the right and top edges of the ruler.

Five reference points for trimming the quarter square triangles

And there’s the perfect quarter square triangle!

Trimmed quarter square triangle

Hopefully this tutorial takes the mystery out of making perfect quarter square triangles. With the help of the Husqvarna Viking Designer EPIC to get those nice straight seams and that scant ¼ʺ seam allowance, making these units was a breeze. Don’t forget to lower that stitch length to 2 as you’ll be slicing through some seams.

Tomorrow, we take a peek at some of the machine embroidery features of the Husqvarna Viking Designer EPIC. Stay tuned – if you think what you’ve seen so far is amazing, it’s nothing compared to what’s coming. Have a great day! Ciao!

This is part 2 of 5 in this series.
Go back to part 1:  Reduce bulk in the seams of your quilt blocks

Go to part 3: Easy to embroider on the Husqvarna Viking Designer EPIC

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Rowena April 13, 2022 - 3:19 pm
Timing is everything, I believe. This tutorial came at the right time, to help me with QSTs. Big difference to the finished product. Thank you.
Carla A. Canonico April 14, 2022 - 1:29 pm
So happy to hear this! Thank you for sharing Rowena!
Rita E. September 25, 2020 - 2:36 pm
I just stumbled upon this post from Pinterest. I've been quilting for years and I'm still learning. This is a great post and great tips Thank you so much for sharing this.
Michele Timms April 30, 2019 - 10:12 pm
This post has been very helpful! Thank you!
Gillian Moore March 28, 2019 - 10:25 am
This is really handy, thank you. X
Irene Hartup February 14, 2019 - 6:32 pm
Thank you for an amazing tutorial.I am a novice quilter and have had real trouble with points and cutting accurate quarter squares.It all makes sense now.Thank you.
Liz Kondelik February 14, 2019 - 1:38 pm
Thank you for the printable tutorial on perfect quarter sq triangles. It was a huge help.
Michelle S October 13, 2018 - 6:00 pm
Thank you so much! I am a beginner/intermediate beginner quilter and took on a project that really was for an advanced quilter. This tutorial was exactly what i needed and I now have perfect QST's. Again, Thanks!
Sarah C August 20, 2018 - 10:06 pm
Love the pictures in the tutorial very visual learner thanks
Donna Jo July 15, 2018 - 8:56 am
Great tutorial for beginners and as a refreshing for an experienced quilter!
MicheleT September 6, 2016 - 6:42 am
Great tips!!! These will be very helpful, thank you!!!
Janie July 26, 2016 - 3:10 pm
Thank you for a great tutorial.
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