beige and blue split half square triangle with title.

Split Half Square Triangles: the easiest method ever

Split half square triangles are a cross between half square triangles and quarter square triangles. They are squares made up of one large triangle and two small triangles. They add interest to triangle blocks and make great pinwheels.

It can be tricky to figure out the sizes that you need to cut, especially with two sizes of triangle, but this method eliminates any difficult math.

It truly is the easiest method ever for making split half square triangles.



Fabric requirements

For this method you need three squares of fabric. They will be the same size as you want your split hst unit to be.

I want my piece to finish at 3″ once it’s in the block (without seam allowances), so I want it to be 3-1/2″ (with seam allowances).

This means cut three squares, all at 3-1/2″. One fabric for the large triangle and two fabrics for the small triangles. I am using the same fabric for the large triangle and one of the small triangles.

two squares of fabric.

First Seam

On the back of the lighter colour square, mark a diagonal line from corner to corner.

Lay two fabric squares right sides together. (The feature fabric and one of the background squares.)

placing light fabric square on blue square.

Stitch from corner to corner, directly on the marked line.

close up of stitching on marked line.

Trim 1/4″ away from the stitching line.

fabric square with diagonal stitching and corner cut off.

Open and press. It’s a half-square triangle.

The piece should still be 3-1/2″ square.

blue and white half square triangle.

Second Seam

Mark a diagonal line on the back of the second background square.

Lay on the half square triangle. Be sure that the diagonal lines are perpendicular to each other.

placing light square on half square triangle.

Like before, stitch directly on the marked line.

fabric square with diagonal stitching.

Trim 1/4″ away from the stitching line.

square fabric with diagonal stitching and corner cut off.

Open and press.

beige and blue split half square triangle.

You’re done!

It’s a perfect split half square triangle with no trimming.

What’s Good

  • easy math
  • simple to cut and stitch
  • no squaring up
  • perfect results

What’s not Good

  • fabric waste
  • only makes one at a time

When to use this method

  • when making small units
  • if you struggle with math
  • if you only need a few units
  • when you’re in a hurry
  • don’t mind the scraps

Rating: 4 out of 5

With half squre triangles, flying geese and quarter square triangles, there are other techniques that have more advantages than the easy method. However, as the pieces get more complex, there are fewer easy shortcuts. For split half square triangles, the easy method is a good option.


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fabric pieces, scissors, pencil and ruler with title "Half Square Triangles".

blue and white flying geese unit 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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