HOW TO MAKE HALF SQUARE TRIANGLES – Simple Half Square Triangles

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So you’re new to quilting and you wonder How Do You Make Half Square Triangles?  I’m here to show you the most outrageously EASY and simple way to cut and sew a half square triangle block.  Half Square Triangles are seriously one of the most versatile blocks to sew and hands down are my favorite.

They are simple, look good in nearly any fabric choices, and can be used to make countless combinations.  

If you don’t want to think about the math, you can find my Half Square Triangle-based quilt – The Maid Modern Quilt in the shop. It is a minimal modern design that comes in baby and throw sizes.

I have several Half Square Triangle Quilts that are currently in the works (you can see the mini quilt patterns here and here), so I decided to do a simple Half Square Triangles Tutorial so you can make some too! There are several different ways to make half square triangles, each having their own pros and cons, so I am going to be doing a series on them this month covering all the different ways to piece HST’s, some quick HST math cheat sheets, the different patterns that can be made using HST’s, and what type of piecing method is best for what type of project.

First, you might ask, What is a half square triangle?

  • A half square triangle is a basic quilting block.
  • It is when you make a whole square quilt block from two half square triangles.
  • The half square triangles will need to have both sides be the same length and the triangles must be the same size as each other to form a square.
  • Often the name of these blocks will be shortened to HST in the instructions of the pattern.
  • Depending on how the half square triangle is cut, the bias edge (diagonal grain of the fabric) will be either enclosed in the seam or on the outside edges of the square.
  • In this tutorial, the bias seam is enclosed in the diagonal seam, which makes it less likely to distort when handling and pressing it.  This is the preferred beginner method.

Ways to Make Half Square Triangles

This is the first installment of the Half Square Triangle Series.  You can see all of the Half Square Triangle Series below:

  1. Method I – Making Half Square Triangles Tutorial – Simple Half Square Triangles
  2. Method II – HST Tutorial 4 at a Time
  3. Method III – The Magic 8 Method – Make 8 HST at Once
  4. Method IV – Make Half Square Triangles from a Jelly Roll – The Strip Method
  5. Method V – How to Use Half Square Triangle Paper
  6. 25+ Half Square Triangle Quilt Patterns


This is the original tutorial that was made several years ago. The graphics are simple and easy to understand. I have updated the post with new pictures and a video including some great tips for more accurate Half Square Triangles. I am leaving the original here, but you can scroll down to find the photo tutorial and new tips.

  1. To make a Half Square Triangles (HST) place two equal-size square Right Sides Together (RST).  Mark a diagonal line on the wrong side of the top fabric square.  
  2. Place the squares RST with the marked square on the top.  Stitch 1/4in on both sides of the marked line.  

3. Cut down the marked line to make two new squares.  

4. Open the half square triangle blocks outward. 

5.  Press seam (both layers) toward the darker color. 

6.  Place a ruler on the block keeping the 45-degree diagonal line over the diagonal seam.  Trim to your square to the desired size.  There will now be two Half Square Triangles (HSTs).


Supplies Needed:

  • Fabric Squares. You can cut them yourself (I have tips for how to cut squares using a Rotary Cutter) or buy 5″ charm squares or a 10″ layer cake to save that step. They usually come in a variety of fabric patterns (usually from a designer’s collection) or can be found in solids, either all in one color in a a color story. Precuts are a great way to just get started sewing, especially if you are new to quilting.
  • Frixon Erasable Pen – this pen erases with heat, so when you press open the quilt block it will disappear.
  • Clear Plastic Quilt Ruler. I prefer a square one to make half square triangles or any square quilt block. The square feature and markings make it much easier to align and square up the quilt block. My go to ruler is from Creative Grids. They are a little pricier than other brands but the way the ruler is designed has made it far easier to use and is definitely my favorite. Going forward I will only buy rulers made by them.
  • Pins or Wonder clips. Wonder clips are quite a bit quicker to take on and off.
  • Rotary Cutter and Mat. My favorite rotary cutter is the Fiskars Designer Series, they are super cute and easy to use.
  • Quilting Sewing Machine Needle – I use a 90/14 when Quilting Needle from Schmetz when piecing with quilting cottons. You can find the Ultimate Guide to Sewing Machine Needles for Quilters with a free downloadable PDF.

This tutorial is essentially the same as the graphic one above but completed in photo steps for those who prefer this method.

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