How to Make Easy Half Square Triangles

Posted by Emily Hammer on

Here's your guide to making pieced half-square triangle units (or sometimes called triangle squares or referred to as its abbreviation HSTs.) Half square triangle units are fun and accurate make with the following simple steps.

Quilters have developed many ways to make quickly piece half-square triangle units. One favorite is this technique, where two squares of fabric are sewn together twice diagonally. When cut apart, the pair produces two identical HSTs.


What Is a Half Square Triangle?
A half square triangle is squares made up of two 90 degree triangles. Each triangle occupies half of the square's space.

Yes, you can sew two triangles together to create a unit. However, it's more comfortable, and usually more accurate, to assemble the patchwork with quick piecing techniques that eliminate the need to handle individual triangles with stretchy ​bias edges.​


What You'll Need:

  • Sewing machine
  • Frixtion Pen or marking pen 
  • Square rotary ruler and cutter
  • Straight pins
  • Iron and ironing board
  • Various fabric scraps


How to make Half-Square Triangles:

For practice, let's use two 5" squares.

1) Place the two 5" squares right sides together.

2) Using the Frixition pen mark, draw a diagonal line from one corner to the opposite corner on the reverse side's lightest color square.
Then draw a 1/4" from the original diagonal line.


(* the blue plastic took is PERFECT because it measures exactly 1/2” to ensure you get perfect lines with slits down the middle of the blue plastic tool to know where to slice.) 

Side note, whatever the finished size HST is, cut squares that are 7/8" larger than the units' finished size.

3) Secure with straight pins.


4) Sew on the two sew lines on the squares.

5) Using your rotary cutter or scissors, slice down the center diagonal line

6) Press the Half Square Triangle Units

Place the half square units on your ironing board, the side with the darkest fabric up. Open up one unit and press carefully, moving the iron into the seam that separates the dark half from the light half.

7) Trim the "dog ears" from the ends of seam allowances.

8) Square up to the desired size


THE BEST PART about HST's is that you can speed up assembly time by chain piecing the squares! Sew many of the HST's together!


I’m happy to help! Ask me questions on our Facebook or Instagram page!


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