Half Square Triangles are seriously so fun to make and easier than they look! Half Square Triangles, or HSTs, are one of the most common quilting blocks and are so versatile in quilting designs.
In this tutorial I’ll be showing how to make Half Square Triangles two at a time using a very easy method – and the most popular! I also share the the supplies I use, a Half Square Triangle math chart, how to chain piece for an efficient work flow, and how to sew HST blocks together.
I first tried out Half Square Triangles when making this quilted needle book (shown above) and found them really fun and addictive to make! It’s a great way to use up scrap fabric and turn them into a knitting project bag, zipper pouch or quilt. My Charm Pack Tote Bag tutorial is made from one charm pack using HSTs (shown above). I also made a quilted fabric book cover using half square triangles and love how it turned out (shown above).
I used the HSTs from this tutorial to make a small wall hanging (below) which would also make such a cute quilt one day! I practiced some hand quilting in the borders before tackling a larger project – like this lap quilt I hand quilted.
If you want some more practice with triangles head over to my tutorial How to Cut and Sew 60° Triangles to learn how! My sewing patterns the Eva Quilted Tote and the Novi Stocking were both designed with 60° degree (equilateral) triangles.
Let’s get the Half Square Triangle tutorial started!
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Some Things You’ll Need
There are some very cool rulers out there that help you cut and trim half square triangles a little faster, but you can totally make them with just a regular quilting ruler and just a few other tools!
- Quilting ruler – My favorite quilting ruler!
- Fabric pen, chalk, or hera marker
- Rotary blade
- Cutting mat
- Coordinating all purpose thread
- Fabric – Quilting cotton is easiest to work with, but linen can be used too (I’m using both in my example)
- Optional: This Bloc Loc ruler is used for squaring up half square triangles blocks. This Omnigrid ruler looks like it does the same thing, but the triangle piece can be repositioned or removed. I haven’t tried either of these but have heard that they can really save time, especially if you need to cut a bunch of half square triangles.
Cut Out Squares
The first thing you’ll need to do is cut out squares in your chosen fabric. (My article How To Cut Squares can help you out with that if you’re new to quilting). And remember two squares get you two half square triangle quilt blocks so keep that in mind when planning your design. If you’re after a specific finished square size, there’s only a tiny bit of easy math to figure it out!
Half Square Triangle Math
To figure out what size to cut the squares out, simply add 1″ (2.5 cm) to the desired finished HST size. A finished HST is when that block has been sewn to the other blocks in a quilt. An unfinished quilt block is 1/2″ (1.3 cm) bigger than a finished block because that seam allowance (usually 1/4″ [0.6 cm]) has been taken away.
Below is a chart with the math already done for you!
Step 1: Draw Middle Line
Take two squares and place them right sides together.
On one of the squares, draw a diagonal line down the middle with a fabric marker (or chalk or hera marker) and ruler. I usually mark the light fabric square so I can see it better. Try to start the line coming right through the middle of the tip at the corners.
Tip: You can use the 45 degree line on the quilting ruler to help you get your line perfectly straight (see picture below).
Another Tip: When I was working with these small 2.5″ squares, I used this tiny 6″ x 1″ quilting ruler to draw the lines (see photos below). It worked out well and I didn’t have to move a larger ruler around.
Step 2: Stitch Two Lines
The line in the middle is your guide line and you won’t be sewing on the line, instead you will sew a scant 1/4″ on either side of that middle line (remember to have your squares right sides together.)
A scant 1/4″ is just slightly smaller than 1/4″ and helps to get more accurate results. Optional: I didn’t use pins in my example, but you could place a few pins to keep the squares from shifting.
Tip: Sew on a scrap piece of fabric first before starting on the square to help keep the angled edges from getting sucked into the machine.
Chain Piecing
Chain piecing is a really great technique if you need to sew a lot of half square triangles for a project. Instead of cutting the thread after each pair of squares, you just continue onto the next pair until. Then simply cut the threads in between after you’ve finished! You can do both stitch lines this way and it really improves the work flow of a project.
Step 3: Cut Along Middle Line
After you’ve sewn along either side of that middle line, next up is to cut along that line you drew. With a ruler and rotary blade, cut right along the middle line from corner to corner.
And now you have two half square triangles!
Step 4: Press
First, press the half square triangle as is (folded in half) to set the seam. Then open it up and press the seams either open or to the side.
Tip: When I was learning how to make half square triangles, this Quilt In A Day square up triangle ruler (Amazon link) kept popping up. The idea is that you can square up half square triangles while the triangles are still folded and then open and press them. Although I haven’t personally tried it (yet), the reviews for this ruler are positive and it seems like a popular option among quilters.
Step 5: Trimming
The last step is to square up the half square triangles and remove the “dog ears” (the little triangle pieces sticking out). Some quilt patterns will have you trim down to a certain finished block size at this point.
To do this, you can use a regular quilting ruler and line up the 45 degree line along the middle seam line (see photos below). Then cut along the two sides to square up the block. Rotate the block to trim down the other two sides. (I switched to my smaller square ruler for this step so I didn’t have to move around my longer rectangle quilting ruler).
Tip: To help save time, This Bloc Loc ruler is designed for squaring up half square triangles in this way. This Omnigrid ruler looks like it does the same thing, but the triangle piece can be repositioned or removed. I haven’t tried either of these but they seem popular among quilters.
And now admire your beautiful half square triangles!
I played around with different layouts using half square triangles and I can see why they are one of the most common and versatile quilt blocks! You could easily make an eye catching quilt using just half square triangles.
That’s the end of the half square triangles “making” portion, but I briefly go over how to sew half square triangle blocks together if that’s something you’re interested in!
Sewing Half Square Triangle Blocks Together
Sewing half square triangle blocks together is pretty straightforward! What I find the most helpful is when the seams are pressed in opposite directions from each other so that the seams “nest together” (you can also press the seams open).
Once you’ve decided on a design, take two half square triangle blocks and place them right sides together (this is also a good time to utilize chain piecing if you have a bunch to sew together). Pin and sew with a scant 1/4″ seam allowance.
I sewed the top two blocks together, and then the bottom two blocks together.
Then, pin and sew the top and bottom “rows” right sides together with a scant 1/4″ seam allowance.
Press your finished block and now you have a larger quilt block design. This pinwheel quilt block is a simple, classic design that I think is really effective in quilts or other projects – and is easier to sew than it looks!
Now have some fun and go make some more half square triangles! Hope you found this tutorial helpful and thanks for reading! 🙂
