Split Half-Square Triangles: the most obvious method

split half square triangles with title.

There are many different methods that can be used to make split half square triangle unit. This method is the most obvious – cutting triangles and sewing them back together.

These triangles are cut from squares. Because the seams are stitched on the bias, it might be a good idea to cut the pieces a little larger and then trim down your finished piece. The measurements given are for exact sizes.

Cut fabric

You will need three squares of fabric. One for each of the triangles.

fabric squares for split half square triangles.

The large triangle is a half-square triangle, so it is actually the smallest square. Cut the square 7/8″ larger than the finished piece will be.

The smaller triangles are quarter square triangles, so the squares will be 1-1/4″ larger than the finished piece will be.

I want my finished units to be 3″ in my quilt, so the square for the large triangle will be 3-7/8″ and the squares for the smaller triangles will be 4-1/4″.

Cutting the fabric

Cut the squares to get triangles.

The cut edges are biases that will stretch easily, so handle with care.

triangles cut for split half square triangles.

It is easy to see how the pieces will go together.

triangles laid out for split half square triangle unit.


Join the two smaller triangles together with a 1/4″ seam.

If you are stitching more than one split hst, keep track of the orientation of these two triangles. It is SO easy to get them switched around, and that will cause problems when you try to join them.

joining small fabric triangles for split HST unit.

Add the larger triangle on the diagonal.

split half square triangle unit.

Open and press.


Once the stitching is done, measure the pieces and square up if necessary.

measuring the split half square triangle unit.

You’re done!

Perfect split half square triangle units.

two split half square triangle patchwork pieces.

Like any method, this method has advantages and disadvantages. You need to decide what is best for your situation.

What’s Good

  • intuitive – obvious construction
  • no marking
  • little fabric waste

What’s not Good

  • need to think about the math
  • bias edges can stretch
  • time consuming to trim to size

When to use this method

  • when you cut and stitch accurately
  • you have a special ruler or die for cutting
  • for scrappy quilts

Rating: 3 out of 5

This method is obvious and easy to do. The big problem is the bias edges. Your finished square has biases on two of the sides. This is manageable if you are careful and use starch, but if you are in a hurry or have to unpick something they will easily stretch and that can’t be fixed.

[mailerlite_form form_id=4]
green and white flying geese units with title.

quarter square triangle with title.

Elizabeth DeCroos - Epida Studio.

Elizabeth DeCroos

Elizabeth DeCroos is the designer and teacher at Epida Studio. She loves to work in quilting, pojagi and embroidery and teach these techniques to others.
Learn more and get her to speak to your group.

Scroll to Top