How to Sew Sixteen-at-a-Time Half Square Triangles!
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Half-square triangles, or HSTs, are used in tons of different quilting patterns. If you ever follow a quilting pattern, chances are you’ll need to make HSTs at some point. One of the most common ways to make half-square triangles is with the four-at-a-time method, which, you guessed it, gives you four HSTs at once.
Today, I’m showing you a different method that will give you 16 half-square triangles at once! This method is similar to making 4-at-a-time HSTs, but you get four times as many blocks out of it, and it’s not that much more work to do.
My Method for Making 16-at-a-Time HSTs
It may seem complicated at first, but the process is simple. You will sew two squares right sides together following the instructions provided, then make 8 cuts to separate out your HSTs. Lastly, you will square up your pieces to make your HSTs into perfect squares.
To follow this tutorial, you’ll need a few simple supplies:
- Quilting cotton
- Straight pins
- Fabric chalk or pen
- Sewing machine
- Matching thread
- Iron & Ironing board
- Rotary cutter & mat (this is a nice set that includes a ruler)
- Quilting ruler
HST Size Chart
You can make these half-square triangles virtually any size. I’ve created a free printable chart that you can download from my Ko-Fi shop with multiple sizes to choose from. The download also includes helpful diagrams that you can reference when cutting your pieces.
Tip: I recommend making a practice set to ensure that your final HSTs will turn out the correct size before using this method for an entire quilt design. This will help you decide exactly what size you need to make the squares so your HSTs turn out the perfect size in the end.
| Size of Finished HST | Fabric Size (2 pieces) |
|---|---|
| 2.5″ HST | 8.5″ squares |
| 2.75″ HST | 9″ squares |
| 3″ HST | 10″ squares |
| 3.25″ HST | 10.5″ squares |
| 3.5″ HST | 11.5″ squares |
| 3.75″ HST | 12″ squares |
| 4″ HST | 13″ squares |
| 4.25″ HST | 13.5″ squares |
| 4.5″ HST | 14″ squares |
| 4.75″ HST | 14.5″ squares |
| 5″ HST | 15.5″ squares |
You’ll notice that the Fabric Size in the chart does not increase at a perfect interval to achieve each finished HST size. The Fabric Size I’ve listed is the closest possible size within 0.5 of an inch that will give you enough room to square up your pieces. You will need to cut off slightly more fabric on some sizes than others to square up your HSTs.
I have the sizes listed this way so you can cut the squares without complicated measurements, and so you have a little room to work with if your stitching or cuts aren’t exactly perfect.
Step 1: Cutting Squares
Begin by cutting out two squares that are the same size as each other. Use the chart to determine what size you need.
Step 2: Drawing Lines
Lay one square of fabric face down (with the wrong side facing you). I like to do this on my cutting mat so I can make straight lines.
Lay a quilting ruler over the fabric and use fabric chalk or a pen to draw a line across the center of the square in both directions. The fabric should be divided into four sections.
Step 3: Preparing Your Squares
Lay your pieces right sides together with the traced lines facing you. The pieces should be perfectly aligned with each other.
If you like, place pins in the center of each quadrant to keep your layers from shifting. For larger squares, you may want multiple pins.
Step 4: Sewing
Next, you will sew around the entire outside of the square with a 1/4″ seam allowance (sew 1/4″ away from the outer edge all the way around). This is shown with teal dashed lines below.
After sewing around the outside of the square, you will sew 1/4″ away from the center lines. Sew next to both sides of each line, as shown with the green dashes above.
Step 5: Cutting
After sewing, you will need to make 8 carefully placed cuts with a rotary cutter, ruler, and cutting mat. You can do the cutting in any order, but this is what works best for me:
1. Cut across the square corner to corner at a 45-degree angle. Repeat this in the other direction.
2. Cut up the center of the square on your traced lines. Do this in both directions.
3. Cut from corner to corner at a 45-degree angle across each of the four points of the square from center line to center line. Do this on all 4 corners.
Step 6: Finishing Your Blocks
Separate out your pieces and open them out. Press each piece with an iron. Be careful to use an up-and-down pressing motion rather than sliding the iron around, which will distort the shape.
After pressing, place the pieces on your cutting mat and line up the ruler in one of the corners. Make sure the piece is straight so the triangles are aligned at a 45-degree angle.
Use a rotary cutter to “square up” the pieces, which means trimming the fabric to make it into a perfect square. You may not have to trim anything if your blocks turned out perfectly square. But you will want to trim off the small corners that extend beyond the square.
I hope you try this and I’d love to see how it goes for you! Let me know in the comments! If you’re looking for more half-square triangle inspiration, check out my scrappy charm pack HST quilt!
