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How to sew 16 at a time half square triangles

How to Sew 16-at-a-Time Half Square Triangles


If you’ve ever made a quilt, you’ll know that half square triangles (HSTs) pop up everywhere. They’re one of the most versatile patchwork units, perfect for star blocks, chevrons, pinwheels and all sorts of geometric layouts.


But trimming and piecing them one by one can be quite time consuming!


So here I’m sharing a great time-saving method: how to make 16 Half Square Triangles at once! This technique is quick, accurate, and great for using up fabric squares you already have cut.

Quilt pattern with brown and pink floral squares. Text: "how to sew... 16 HST's at a time." Playful arrow and squiggle.

You’ll Need

  • Two fabric squares (one light, one dark)

  • Rotary cutter and ruler

  • Pencil or fabric marking pen

  • Cutting mat

  • Sewing machine

  • Iron and pressing mat


Step 1: Cut Your Squares


To make 16 HSTs at once, start with two equal-sized fabric squares.


For this tutorial, I started with 14" squares, which give an unfinished size of around 3½" - 4", depending on how much you trim. I prefer to trim just a little to avoid fabric waste, so my HSTs finished at 4".


Step 2:

Place your two squares right sides together.

Sew around the four sides using 1/4" seam allowance.


Floral fabric square with sewing instructions: start with two 14" squares, sew right sides together, 1/4" seam. Beige background.

Draw a vertical and horizontal line, centrally, so your square is divided into 4 equal sections. These will become your sewing guides.


Floral fabric square with drawn vertical and horizontal lines. Text instructs to "draw halfway" and "sew 1/4" down both sides."

Sew a seam ¼" away from each side of both diagonal lines.



Step 3:

Cut along the drawn horizonal and vertical lines.

Cut diagonal lines from corner to corner, creating an “X”.


Fabric with floral pattern is cut into triangles. Text instructs to "cut along the drawn lines" and "cut diagonally." Rotary cutter illustration.


Step 4: Sub Cutting


Cut each quarter diagonally.


Patterned fabric with red flowers is divided into triangles. Yellow arrows point to cuts. Text reads "cut each quarter diagonally too."

You’ll end up with 16 small triangle units.


Step 5: Press and Trim


Open each triangle and press the seam allowance towards the darker fabric (or whichever direction gives less bulk).


Trim each HST to your desired unfinished size (4").

Bright pink and brown patterned fabric squares arranged. Text guides assembly for a sewing project with steps on pressing and trimming.

Step 6: Arrange and Sew

Now for the fun part - arranging your HSTs into a block!

Try:

  • Pinwheel (classic and dynamic)

  • Diamond layout (great for modern quilts)

  • Flying geese rows or zigzags


Once you’ve settled on your layout, sew them together in rows, pressing as you go.


Patchwork quilt pattern of vibrant pink and brown floral fabric arranged in a grid with intricate flower designs and swirling motifs.

Tips for Perfect HSTs

✨ Starch your fabric before cutting to reduce stretching

✨ Press, don’t drag your iron, especially since the edges are on the bias

✨ Trim consistently to make your final block sit flat and neat.


That’s It!

You’ve just made 16 perfect HSTs - all from two squares of fabric!

Once you’ve tried this method, you’ll never go back to sewing them one by one. It’s perfect for scrappy quilts, star blocks, or when you just want to make a big batch in one go.

I've used these quilt block to make ruffled cushion covers -


Two colorful, patterned cushions on a light gray armchair. One cushion has pink and green floral designs. Green plant in the background.

Have you tried the 16-at-a-time method before? Let me know in the comments or tag your blocks with @whatkimberleymakes so I can see them!


Happy sewing!

Kym

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