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Half-Square Triangle Pillow Pattern

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How to make an easy Half Square Triangle Pillow. This simple tutorial includes a free pattern and measurements to sew three different size pillows. 

half square triangle pillow

Easy Half Square Triangle Pillow

Half square triangles are one of my favorite types of blocks to use in sewing projects.

They’re easy and so fun to make and can be used for quilts, pillows, placemats, you name it! Today I’ll show you how to sew an envelope pillow made out of half-square triangles.

It’s quick and easy – perfect for seasonal decor or even gifting!

Today’s pillow project will walk you through creating the front of the pillow and then putting it together with additional fabric to make an envelope-style pillow cover. (I prefer envelope-style pillows covers, they are so much easier than installing a zipper.)

8 half square triangle blocks at one time

I’ve got a great half-square triangle sewing hack that with a few sewing lines and cuts of your rotary blade you will create 8 half square triangle blocks at one time.

It’s a fabulous sewing hack that really speeds up the process of making this half square triangle pillow project.

Fabric used 

In today’s project, I use a charm pack from Robert Kaufman’s Kona Palette line called Wildberry. I love using the Kona Palettes. They com already curated in such pretty colors and you can get them in fat quarters, jelly rolls, layer cakes,and charm packs.

fabric used in half square triangle pillow

Pattern variations

The pattern as written is a block of 1.5 inches (finished size) half-inch square triangle blocks are sewn together with a border. It’s a very simple project and you can change it up anyway to suit your tastes. 

  • Use larger half-square triangle blocks.
  • Skip the border (It may take some math to figure out how many blocks are needed to get your desired pillow size.)
  • Add a bit of trim to the edge of the pillow. 
  • Quilt the front pillow piece. (my pillow form was white, so I did not feel the need to quilt the front side, however, if you are covering a pillow that is dark or has some sort of design, adding a layer of batting will completely disguise the pillow below. Just use a bit of quilt basting spray to adhere the front piece to the batting and quilt the pillow block as desired. then assemble as directed in the tutorial below.
  • Use any combo of solids or prints. (this project is a great stash buster)

Tips:

  • I recommend using a scant quarter-inch seam allowance when sewing the lines down the squares. (when making the half square triangle blocks.)
  • Don’t skip the squaring up of the half-square triangle blocks. Because they are so small it important the squares are the correct size to line up properly.
  • Use spray starch when pressing to help keep the squares from stretching out of shape.

How To Get The Perfect Quarter Inch Seam Allowance

When working with squares this small it is important to have an accurate seam allowance. Every time I start a project, I line my needle up using a seam allowance ruler (I did try the one with the seam allowance guide, but it did not work well for quarter-inch seams on my machine due to the placement of the feed dogs.)

seam allowance ruler and foot

I have also been using this quarter-inch foot with the guide. (just choose one that fits your machine.) I still use the seam allowance ruler with this foot and I find that I do still have to move my needle over just a bit for a perfect quarter-inch seam allowance. However, once I have made the adjustment, the guide helps keep all my seams perfectly aligned. 

How To Square Up Your Half-Square Triangle Blocks

I tested two new rulers for squaring up my blocks. I liked them both for different reasons, so I don’t think I had an overall favorite.

half square triangle rulers

The perfect 5 ruler from creative grids. I liked this one because you can do multiple sizes (up to 5 inches). This ruler also has sticky/grabby patches on the back that really hold the fabric in place and prevent sliding. To use it, you just line the diagonal of your block up with the diagonal line and then use the grid lines to trim to the size needed. (this ruler also comes in a “perfect 10” size.)

Bloc Loc 2.5″ Half Square Triangle Ruler. I liked this one because it has a little groove that “locks” to the seam of your half square triangle. I found this ruler would slide a tiny bit if I added too much pressure when cutting, but It was very easy to use. If price were no object I would buy this ruler in a few different sizes, but they are pricy compared to the perfect 5 rulers.

You can see the comparison in the video I attached to this post.

For larger squares, I am still using my June Tailor Perfect Half-Square & Quarter Square Triangle Ruler.

How to Sew a half Square Triangle Pillow

Fabric Amounts Needed for Various Pillow Sizes

  • 16 x 16
    • 8 different colored 5-inch squares
    • 8 solid background 5-inch squares (I went with white) to make 64 half-square triangle blocks
    • 2 strips 2.5 by 12.5 (for the border)
    • 2 strips 2.5 by 16.5 (for the border)
    • 3/8 yard fabric for the back of the pillow
  • 18 x 18
    • 10 different colored 5-inch squares
    • 10 solid background 5-inch squares (to make 100 half-square triangle blocks)
    • 2 strips 2 by 15.5 inches (for the border)
    • 2 strips 2 by 18.5 inches (for the border)
    • 1/2 yard fabric for the back of the pillow
  • 20 x 20
    • 12 different colored 5-inch squares 
    • 12 solid background 5-inch squares (to make 120 half-square triangle blocks)
    • 2 strips 2.25 by 17 inches (for the border)
    • 2 strips 2.25 by 20.5 inches (for the border)
    • 3/4 yard fabric for the back of the pillow

materials needed

Seam allowances are .25 inches

Instructions:

Step 1: Create the half-square triangles.

This shortcut method produces 8, 2-inch half-square triangle blocks.

Line up one white 5-inch square with one colored 5-inch square.

Use a ruler and draw a line diagonally from corner to corner.

Sew a scant 1/4 inch seam on both sides of the lines you drew. (As shown below.)

how to make 8 half square triangles at once

Use your rotary cutter and cut the square in half in both directions. (As shown below.)

how to make 8 half square triangle blocks at once

Then split the smaller squares apart. (Cutting along the original lines you drew.)

how to make 8 half square triangle blocks at once

Open the half-square triangles and press the seams towards the darker fabric.

half square triangle blocks

Trim up your squares to 2 inches,

how to make a half square triangle block

Step 2: Sew the Half Square triangle blocks together.

Line the squares up according to the pattern. 

Sew the blocks together, one row at a time. Press the seam allowance to the darker side.

To keep the rows from getting “wonky,” I suggest sewing the blocks together in groups of two. (see diagram below.) 

Then sew the rows together. It helps to nest the seams of the blocks. (Even if they are not pressed the same way I was nesting.)

Press these seams open to help reduce bulk.

 Trim up any uneven edges so your square is perfectly square.

Step 3:  Add Borders.

Line up the shorter strips along the top and bottom of the half-square triangle block and sew together with a quarter-inch seam allowance. Press the seams flat.

Line up the longer strips on the other sides and sew together with a quarter-inch seam allowance. Press these seams.

Step 4: Sewing the back of the envelope Pillow Cover

Cut 2 pieces of fabric according to your pillow size:

  • 16 x 16: cut 2 pieces 16.5 x 11.5 inches
  • 18 x 18: cut 2 pieces 18.5 x 13 inches
  • 20 x 20: cut 2 pieces  20.5 x 14.5 inches

Hem the “envelope” edges by folding the edge over .25 inches, press. Fold another .25 inches, press again and sew along the pressed edge. 

Repeat for the second piece.

Line up the raw edges of the front piece and the two back pieces right, sides together. The hemmed edges will overlap. (as shown below) Sew all the way around with a .25 inch seam allowance.

Flip the pillow cover right side out.

Give the edges a final press.

Add a pillow form and you are done!

More Easy Quilting Projects

Did You Sew a Half Square Triangle Pillow?

If you end up sewing one, be sure to come back and leave a star ⭐️⭐️⭐️⭐️⭐️ rating and/or a review in the comments section below. If you share an image on Instagram, be sure to tag me and use #scatteredmompatterns! You can also share an image to my private Facebook sewing group!

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Yield: 1 half square triangle pillow

Half-Square Triangle Pillow

Half Square Triangle Pillow

How to make a pillow using half-square triangle blocks. This simple tutorial includes a free pattern to sew three different size pillows. 

Prep Time 5 minutes
Active Time 3 hours
Total Time 3 hours 5 minutes
Difficulty easy/intermediate

Materials

  • Fabric (see amounts in the post)
  • 16-inch pillow form
  • Ruler
  • Rotary Cutter
  • Marking Pen
  • iron
  • Seam ripper (Yes, you may end up needing a seam ripper if you sew any of the squares backward or upside down like I did, lol)

Instructions

Step 1: Create the half-square triangles.

  1. This shortcut method produces 8, 2-inch half-square triangle blocks.
  2. Line up one white 5-inch square with one colored 5-inch square.
  3. Use a ruler and draw a line diagonally from corner to corner.
  4. Sew a scant 1/4 inch seam on both sides of the lines you drew.
  5. Use your rotary cutter and cut the square in half in both directions.
  6. Then split the smaller squares apart. (Cutting along the original lines you drew.)
  7. Open the half-square triangles and press the seams towards the darker fabric.
  8. Trim up your squares to 2 inches,

Step 2: Sew the Half Square triangle blocks together.

  1. Line the squares up according to the pattern. 
  2. Sew the blocks together, one row at a time. Press the seam allowance to the darker side.
  3. To keep the rows from getting "wonky," I suggest sewing the blocks together in groups of two.
  4. Then sew the rows together. It helps to nest the seams of the blocks. (Even if they are not pressed the same way I was nesting.)
  5. Press these seams open to help reduce bulk.
  6.  Trim up any uneven edges so your square is perfectly square.

Step 3:  Add Borders.

  1. Line up the shorter strips along the top and bottom of the half-square triangle block and sew together with a quarter-inch seam allowance. Press the seams flat.
  2. Line up the longer strips on the other sides and sew together with a quarter-inch seam allowance. Press these seams.

Step 4: Sewing the back of the envelope Pillow Cover

  1. Cut 2 pieces of fabric according to your pillow size:
  2. 16 x 16: cut 2 pieces 16.5 x 11.5 inches
  3. 18 x 18: cut 2 pieces 18.5 x 13 inches
  4. 20 x 20: cut 2 pieces  20.5 x 14.5 inches

Hem the “envelope” edges by folding the edge over .25 inches, press. Fold another .25 inches, press again, and sew along the pressed edge. 

  1. Repeat for the second piece.
  2. Line up the raw edges of the front piece and the two back pieces right, sides together. The hemmed edges will overlap. (as shown below) Sew all the way around with a .25 inch seam allowance.
  3. Flip the pillow cover right side out.
  4. Give the edges a final press.
  5. Add a pillow form and you are done!

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One Comment

  1. I have never seen this technique to make half square triangles, before, but it’s AMAZING! Thank you for this tutorial!