Half Square Triangles (HST)

HSTs are versatile components of many quilt blocks, and are both simple and quick to make. In this tutorial I’ll give you two methods to make either one HST at a time, or to make two at a time.

Before we start, you should understand the difference between a FINISHED block measurement and an UNFINISHED block measurement. Finished measurements literally mean when the block is finished – as when a block is completely sewn into a quilt. And unfinished measurements literally mean before the block is sewn – and are generally 1/2″ bigger than the finished size, in both directions – to account for the 1/4″ seam allowance. This is important to know, since as you cut the fabric, you’ll be cutting at the unfinished size. Most patterns allow for this, but if you’re making up your own block, you’ll need to consider it. Hopefully this makes sense, but if not, I think it will as we go along.

Cut Squares (One of Each Color)
Two At A Time1″ larger than desired finished size
One At A Time1/2″ larger than desired finished size

Two At Once Method

Let’s start with making two identical HSTs at once. In these examples, let’s say we want to make 4″ finished HSTs (4.5″ unfinished). So as the chart above states, we will cut our squares one inch bigger than the finished size. Specifically, two 5″ inch squares, one of each color.

Next, place one square on top of the other, right sides together (RST). Then draw a line diagonally from corner to corner on the back of one of the squares. I usually put the lighter color on top, just because it makes seeing the line a little easier. You can use a pencil, or your favorite fabric marker for this – I usually use a Frixion pen.

I often put a pin across the drawn line until I can get the block to my machine, but you can skip that step if you’re a no-pin quilter. Now for this method, where you get two HST, sew ON EITHER SIDE of the drawn line 1/4″ away. In the photos below you can see my laser line is 1/4″ away from the drawn line – but if you don’t have a laser just use your 1/4″ foot and you’ll be fine. In the second photo you can see where I have the very tip of the block lined up with my little purple mat that sits on the bed of my machine (best invention since sliced bread, this one is a Baby Lock product, but I’m sure there are others out there).

In the photo below you can see the finished seams on both sides of the drawn line.

The next step is to cut the two HST apart directly on the drawn line.

There are a few methods to trim the HST to the correct size. The first method requires a special ruler, called Clearly Perfect Slotted Trimmers. I love this little ruler and use it frequently. It comes in a package with two – one for whole number HSTs and one for half inch HSTs. This makes life easier, but is not absolutely necessary to making HSTs – the second trimming method below uses a regular square ruler, so have no fear.

For the first method, in the photo below, I’m using the 1/2″ Trimmer ruler. Note the red arrow pointing to the 4.5″ line on the ruler – this is lined up ON THE SEAM along the bottom of the HST. Then simply trim off the little bit of over hang, and use the little slots on the sides to cut off the dog ears. Voila! A 4.5″ unfinished HST. Now press the HST open – either press to the darker fabric, or if you like, press the seam open.

For the second trimming method, use a regular square ruler. Line up the 4.5″ line ON THE SEAM at the corners (since we are making 4.5″ unfinished HSTs).

Then as in the previous example, trim off the over hang. Remove the ruler and trim off the dog ears as well.

I prefer these two methods, where you trim the HST before you press it open – it’s quicker, the dog ears are trimmed beforehand, and I think it’s more accurate. Sometimes I found I stretched the HST out of whack as I pressed it open, therefore it wasn’t always square when I trimmed it open.

And here are the resulting TWO identical 4.5″ unfinished HSTs.

One At A Time Method

Cut Squares (One of Each Color)
Two At A Time1″ larger than desired finished size
One At A Time1/2″ larger than desired finished size

And on we go to the one at a time method. Here is the same chart again. Remember we are making 4″ finished (4.5″ unfinished) HSTs. In this method, we begin with a smaller squares, 4.5″ one of each color – as the above chart shows we are starting with squares 1/2″ larger than the finished size.

As before, place squares RST, with lighter fabric on top. Again draw a diagonal line from corner to corner.

However, this time, sew DIRECTLY ON THE DRAWN LINE. Not on either side like we did in the two at a time method. You can see my laser tracking right along the line below.

Place a ruler with the quarter inch line ON THE SEAM and trim away the extra fabric on the right. This extra fabric is now waste – or scrap fabric for your stash, depending on your point of view.

As you can see, with this method, there is little to no trimming necessary, not even dog ears!

Press open as before – either to one side, or open, whichever you prefer.

And there you have it, two methods with the same results. Here are all three 4.5″ unfinished HSTs we just made together. Thanks for reading, if you have questions or comments, don’t hesitate to reach out to me. I’m happy to help if I can!