Half square triangles, referred to by the quilting acronym HST, are a staple to make for many quilt block patterns. It is a simple but effective design where two triangles are sewn together to create a perfect square. You can build up so many great quilting patterns with these including hour glasses, pinwheels, stars, zig zags and lots more. Since so many patterns rely on knowing how to make half square triangles, it is worthwhile to learn how to make them quickly and efficiently.
The traditional method of making these is quite slow and laborious. It involves cutting out two squares from different fabrics, cutting each square in half diagonally and then sewing together the separate triangles to make up new squares featuring two contrasting colors or patterns.
Another way is to use a triangle quilt ruler to use as a template. You can cut around the ruler with a rotary cutter or trace around and cut with scissors to make each individual piece. Then the fabrics are sewn together to form the squares that you need. Again, this can take time and it is easy to make mistakes with all the cutting required.
The method demonstrated here can speed up cutting and sewing all your pieces since you are creating 4 at a time. It's not the only way to make multiples of half square triangles but it is an easy way that is ideal for beginners to use.
1: Choose the Fabrics and Cut Out Squares
Part of the fun with quilting is to choose the fabrics that you will use for each project. With the half square triangles, I look for contrasting yet complementary fabrics to build each square. Many quilters use one patterned design and then a solid color that picks up on one of the shades running through the motif in the other fabric.
I chose a beautiful peacock feather design in blue that has some golden highlights. I could have matched it with a plain blue which would make for a very dark looking block so instead I chose a plain golden color cotton that really complemented it.
Tools and Materials Needed to Make the Half Square Triangles:
- Two contrasting fabrics
- A rotary cutter
- Cutting mat
- Square quilting ruler
- Sewing machine
- Glass head sewing pins
- An iron to press your pieces
First you need to cut out two squares of the fabric that you want for your triangles. The easy way to cut out the squares is to use a square quilting ruler as a template. Many quilting rulers are now compatible with rotary cutting which makes the cutting process quicker. Place the fabric on top of a cutting mat and then position the ruler over the fabric exactly where you want it. Hold the ruler down with one hand and cut around it firmly with a rotary cutter.
An alternative method to using a rotary cutter is to mark out a square using tailor's chalk or a water-soluble fabric marker. You can then cut out your pieces using scissors instead.
In order to make four half square triangles at a time, make your initial squares fairly large. I chose a 6 x 6 inch size but you could opt for bigger than this. Unless you’re working on a mini quilt you will probably want to stick to this size or larger.
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2: Pin the Squares Together
Pin the two squares of fabric together with the right sides placed on the inside and the wrong sides showing on the outside. Try and position the edges neatly so they are in perfect alignment.
I like to use glass head pins for quilting because they are not affected by a hot iron when you need to press seams whereas acrylic head pins can melt and spoil the fabric.
3: Start to Sew Down One Edge
The next step is to sew the pinned squares together. Choose a straight stitch on your sewing machine. If you have a special quarter-inch quilting foot for your sewing machine, then this is the best choice of foot to use. Otherwise you can simply use a regular straight stitch foot. I used a red sharpie pen to highlight where the a 1/4 inch measurement is on my regular foot so I can easily see the mark and line it up against the edge of my fabric when sewing. 
You need to start sewing 1/4 inch down from the top of your fabric and the same distance across from the side edge. It isn't necessary to measure the side edge if you are using the special quarter-inch quilting foot or similar marker. You can mark this position with a fabric marker if you are not confident in doing this by eye. Start sewing in a straight line all the way down the square until there is roughly 1/4 inch left then stop.
4: Sew Around All the Edges
Rotate the fabric around and sew down the next side of the square using the same process as before. Stop at the 1/4 inch point before you rotate again and sew the next seam. You will end up sewing all around the sides of your square just as you can see in the photo displayed above. At this point, you may have concerns that it all looks wrong but the trick to this technique comes with the cutting.
5: Cut the Square in Half Across the Diagonal
Now you need to cut your square in half diagonally which means cutting it from one corner in a straight line over to another. You can mark the diagonal line first with a ruler and a suitable fabric marker and then cut along the traced line with scissors. Alternatively you can use a ruler on top of a cutting mat and cut the fabric with a rotary blade. I used my rotary cutter which makes a very clean cut.
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6: Cut each Triangle in Half
If you place the cut pieces back together, you can then make a second cut diagonally across the other way from one corner to another. Now you’ve created 4 smaller triangle sections out of one larger square.
7: Press the Seams
Carefully open out each piece and lightly finger press down where the sewn seam is. You want to press the seam underneath the darker of the two fabrics. If you press the seam under a lighter colored fabric, there is a risk that it will show up more and affect the look of your finished quilt. This is known in the quilting world as pressing to the dark side and it's a good habit to get into.
Now lightly press each piece with an iron. Make sure to only press down, and not rub over the fabric as rubbing can stretch your sewn squares out of shape. Some quilters use starch to help keep the shape but I prefer not to. Snip off the unwanted pieces known as dog ears which occur at the corners where the seam is sewn.
If your pieces don’t all measure the same once pressed, you are probably stretching them at the ironing stage. You can always trim the pieces back to size if this occurs. I like to press pieces on my portable ironing board which I keep in my sewing room.
Half Square Triangles are Easy to Make with this Method
The technique demonstrated here is a quicker way to make up half square triangles for your blocks than making each piece individually. The benefit of making four at a time is that it is easier and quicker than traditional methods. One potential downside is if you do not wish to have all these pieces made from the same choice of two fabrics.
To make the process even faster, consider first pinning multiple squares together and then doing all your sewing in one go before moving on to the cutting. Using a batch process with repetitive techniques like this can speed things up even more.
Image Credits: The introductory image belongs to the author, Marie Williams Johnstone. All other images (unless watermarked with the author’s name) are product photos from Amazon.