Sewing Half-square Triangles (New Skill)

What is a 'half-square triangle'?

It is a square that is made up of two right-triangles.

There are a many ways to make half-square triangles. I'll show you two.

Method 1
Step 1: Cut two squares of fabric the same size. Mine are 5" square because the next block we are making is a Shoo-fly block and that is the size we will need.

Step 2: Draw a line (I used a pencil) from one corner to the opposite corner on the lightest colored square.

Step 3: Stack the two squares, right sides together. I usually pin them together so they don't shift while I am sewing.

Step 4: Sew 1/4" on either side of the drawn line.

Step 5: Cut along the drawn line.

Step 6: Press open (usually press towards the darker fabric) and you will have two half-square triangles.

Here's a video:


Method 2
Step 1: Cut two squares of the same size. These are 7" square because the Shoo-fly block we are making next needs four 4 1/2" half-square triangles.

Step 2: Pin in a few places (I used 4 pins) to keep the blocks from shifting while you are sewing. Sew 1/4" from the edge of the block all the way around.

Step 3: Cut through the center of the block from corner to corner.

This is what the block looks like after the first cut.
Don't separate your triangles like I did for the photo!
I just wanted you to see where the cut was.
Keep the two halves together and rotate your ruler to cut the second diagonal.

Step 4: Cut the other diagonal. Again, I pulled them apart so you could see the second cut.

Step 5: Press the triangles open. The cut edge is a bias edge so be careful to PRESS instead of IRON or you will distort your block. Press towards the dark side.

Step 6: Trim your block to 4 1/2" making sure that the diagonal line of your block lines up with the diagonal line on your ruler.

(4) Half-square triangles ready to sew into your Shoo-fly block!

 Here's a video for Method 2:

Printable directions! Click on the image to view full size and print from your browser window.

Printable directions! Click on the image to view full size and print from your browser window.

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