Half-square Triangle Tutorial featuring the easiest method for this quilt unit

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

A half-square triangle, or HST, is a common quilting term for a square made up of two triangles joined together on the diagonal.  It is one of the most common units of a quilt block, probably second only to a plain square.  They are used in many quilt blocks, like the shoo fly or the churn dash.  There are many ways to make these, but this method is the easiest one ever.

Cut squares of fabric

Begin with two identical squares.  Make them each the same size that you want the final square to be.  For example, if you want to make 3-1/2″ squares, cut each of these 3-1/2″ square.  When you join it with other pieces, it will finish at 3″ since it has the standard 1/4″ seam allowance on all sides.

two squares of different colour fabric.

Mark with a diagonal line

Lay the squares right sides together.  Using a ruler, draw a diagonal line from one corner to the opposite corner.

drawing a diagonal line on a piece of fabric


Sew right on this line.

square of fabric with a diagonal line of stitching.


Trim off one of the sides (it doesn’t really matter which one).

square of fabric with one side cut off.


Open and press the seam to the dark side.  The square should be accurate to the original size that you cut.

fabric square made by joining a triangle of green and a triangle of grey on the diagonal.

That’s all!

What is good about this method

  • The math is super simple – just add the regular 1/2″ seam allowance for the square.
  • No dog ears (tiny triangles sticking off the corners)
  • No trimming to size – it’s automatically the right size.

What isn’t good

  • There’s a lot of waste fabric.  The cut-off side of the square is waste.  You can join them to make a smaller HST block, but it’s unusual to have a pattern that will use both sizes.  More often than not, they become “bonus” pieces that go into your stash waiting to be used in a new project.  If that’s what you want, it’s fine, but for some people it’s more stressful.

Rating: 3 out of 5

I think this method is great for beginners or people who struggle with arithmetic.  It works if you are in a hurry and have lots of fabric to spare, but it is not my favourite method.


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

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.

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