split half square triangles with title.

Split Half-Square Triangles: the most popular method

Split half square triangles take triangle piecing to the next level. They are fun to use in quilt blocks, but are more complex to put together. This popular method makes construction easy.

This method makes four pieces at a time, but be sure to read to the end to see the caveats about using them.

Fabric requirements

The hardest part of this method is figuring out what size squares to cut.

you need:

  • one square of feature fabric and one square of background fabric 2″ larger than you want the finished unit size to be
  • two squares of background fabric 1″ larger than you want the finished unit size to be
squares of fabric.

I want my finished units in my quilt to be 3″ square (without seam allowances). That means that I cut the small background squares 4″ and the large background and feature squares 5″.

First Seam

If you have made half square triangles, you have probably seen this method before.

Mark the back of the larger background fabric square with a diagonal line.

Stitch 1/4″ away from the line on both sides.

stitching 1/4" away from diagonal line.

Trim directly on the line.

fabric square cut on diagonal.

Open and press. You will have two half square triangle pieces.

green and beige half square triangles.

Trim these down to 4″ square.

squares up half square triangles.

Second seam

Mark the back of a smaller background square.

Lay it right sides together with one of the half square triangle pieces. Make sure the diagonal lines are going in opposite directions.

Stitch 1/4″ away on both sides of the line.

square with diagonal stitching.

Cut apart directly on the marked line.

fabric square cut on the diagonal.

Open and press. You have two split half square triangles.

two split half square triangles.

Repeat with the other half square triangle piece and background fabric.

Trim to 3-1/2″ square.

Finished pieces

The result is four split half square triangles, but they are in pairs of mirror images.

four split half square triangles.

You will have to decide if you want to use these four units together or not. It depends how sensitive you are.

split half square triangle pinwheel layout.

Like any construction method, this one has good and bad points. You have to decide what you like best for your situation.

What’s Good

  • easy constuction
  • makes four at a time
  • little waste

What’s not Good

  • results are not identical
  • need to square up

When to use it

  • if you don’t mind the mirror image
  • if you are need a lot of units

Rating: 4 out of 5

This method has a lot going for it, as long as you can get over the mirror image. You could always make two projects, and use split the pieces up so they’re all identical.


blue fabric pieced triangles with title "half square triangles".

two quarter square triangles with title.
Elizabeth DeCroos

Elizabeth DeCroos

designer, teacher, speaker

Elizabeth enjoys doing all types of sewing and needlework and teaching others new techniques. For more information or to have her speak to your group click HERE.

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