How to Easily Make Half Square Triangles - 3 Simple Methods

Half square triangles quilt tutorial


Half square triangles are a quilting staple. They are used in many different quilt blocks such as the Pinwheel, Ohio Star and Square in a Square Blocks, just to name a few. They can be arranged in infinite ways and lend themselves to both traditional and modern designs. These little gems are a must-have for your quilting repertoire! In this tutorial, I will be sharing three methods to easily make half square triangles (HST). 

Basic Tools for HST

Before we get to the nitty-gritty, let's take a look at the tools you will need:


Easily Make Half Square Triangles


You will need a rotary cutter, a straight edge ruler, a pencil for drawing diagonal lines and a square ruler for trimming your HST. For trimming there are many choices. You can use a standard quilter's square ruler as is used to square up quilt blocks (shown bottom left), or you may choose a specialty ruler made for HST such as the Dragonskin Resize-it Template Set (shown top right) or the Bloc-Loc Half Square Triangle Rulers (shown bottom right). If you will be making a lot of HST or making them frequently, a specialty set is well worth the investment. While not necessary, a rotating cutting mat can be very helpful for trimming your squares as well.


There are three basic methods for making HST: 2 at at time, 4 at a time and 8 at a time. Which method you choose depends on several different factors.

The 2 at a time method is also referred to as the basic or standard method. This method is the slowest of the three, but it produces the most accurate results. It's perfect for beginners. It's also the best method if you need large HST's. 

The 4 at a time method is a faster way to make HST's but, it has its drawbacks. Cutting your HST's this way will create bias edges, making your triangles prone to stretching. You can mitigate this by using starch on your fabric before you cut your squares, but extra care will still need to taken as you sew and press them. Also, because you will be cutting through your stitching line, there is always the chance the stitching will unravel at the edge. This can be solved however, by using a smaller stitch length.

The 8 at a time method also known as the Magic 8 method and is the fastest method. The drawback here is that the speed you gain may be offset by more bias instability and more complex cutting calculations. 

For all three methods, you will be cutting your squares a little larger than you need them and trimming the squares to the exact size you need afterwards. Since trimming is the same for all three methods, please scroll to the bottom of the page for trimming instructions. 

2 at a Time Method

Fabric Cutting - Cut squares 1" larger than the finished HST you need. For example, if you need a 2" finished HST, cut two 3" squares. Note - a 2" finished HST (as measured after it is sewn into the block) is 2.5" unfinished. Its easy to mix these up so be clear that you are adding 1" to the finished size you need.

Draw a diagonal line on the wrong side of the lightest square:


Easily Make Half Square Triangles


Place the two squares right sides together and sew 1/4" from the drawn line on each side:


Stitch on both sides of line


Cut along the drawn line:


Cut along the drawn line


Carefully press them open, pressing the seam toward the darker fabric:


press open the hst


4 at a Time Method

Fabric cutting - You will need to know the size of your unfinished HST. For example, a quilt pattern may call for 2 - 3" HST's. This is the trimmed (unfinished) size. (When it is sewn into your quilt block, it will be 2.5", which is the finished size.) You then divide the size of the unfinished HST by .64 to get the size of the starting square. In this case, 3 divided by .64 = 4.6875. I like to round up on the generous side to be sure there will be enough excess for trimming, so I would round up to 5". You could just round up to 4.75", but be aware this may be very close...I like more wiggle room in my HST measurements!

Lay your two fabric squares right sides together and sew around the perimeter with a 1/4" seam:


HST sew around the perimeter


Draw two diagonal lines across the block, having the lines intersect in the center. Cut through these diagonal lines:


cut on diagonal lines for 4 at a time HST


Four HST's ready to trim:


4 HST ready to trim


8 at a Time Method

Fabric Cutting - For cutting the 8 at a time method you start with the finished size of the HST. The formula is - finished size + 1" X 2 = size of the cut square. For example, if I need the finished size to be 2", the formula would be 2" + 1" x 2 = 6". I would start with 2 - 6" squares.

Start by drawing diagonal lines from corner to corner on the lightest square:


8 at a time HST draw diagonal lines


Sew 1/4" from both sides of each line:


8 at a time HST sew along diagonal lines


Cut across the center of the square, both vertically and horizontally. Be sure to measure carefully so you cut exactly on the center. 


8 at a time HST cut vertically and horizontally


Then cut along the diagonal lines:


8 at a time HST cut on diagonal lines


Eight completed HST's:


8 at a time method completed HST



In the example below, I am using a rotating cutting mat. As stated before, while not necessary, this tool makes the job much easier.

Place your square ruler on the HST, lining up the center diagonal seam line. Cut along one side and across the top.


Trimming HST on rotating cutting mat first side


Rotate the mat 180 degrees and cut along the side and top again:


Trimming HST on rotating cutting mat second side


I hope this tutorial has been helpful! If you play around with the different methods, you will soon discover your favorite method and also get a feel for which method best suits your skill level and current project. 

Happy Quilting!

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