How To Make Half-Square Triangles In Quilting

Do you want to know how to make half-square triangles in quilting? Then this is the post for you! Half-Square Triangles, commonly called HST, are everywhere! And so are quarter-square triangles (QST)! It seems as though I make them all the time, so I finally came up with a quick, and accurate, method to do so. In this blog post I’ll teach you how to cut half square triangles for quilting and how to make quarter square triangles in quilting.

Before we go on with the tutorial, let’s start with the basics. What are half-square triangles? Half-square triangles, or HST as they are commonly called, are squares of fabric made up of two equal triangles.  The image below the heading of this blog post is an example of a half-square triangle.

Another common triangle in quilting is the half-quarter square triangle, commonly called HQST. Half-Quarter Square Triangles (HQST) are made up of three triangles, with the largest triangle being twice as big as the two smaller ones. Refer to the sample image at the bottom.

This method may not be the most efficient method for how to make half-square triangles in quilting, nor may it be the fastest. But at this point in time, it’s my favorite, because it’s fast and easy. And that’s what counts. I always recommend you use methods and techniques you are comfortable with when quilting.

Each HST is made up of two triangles.   These triangles are referred to as T1 and T2.  So, if you like math, T1 + T2 = HST.  In the image above, the top triangle (green) is T1 and the bottom triangle (purple) is T2.

It is important to note that one should use a scant 1/4″ seam allowance when making these.  What’s a scant 1/4″?   It’s sewing a few threads short (smaller) than a “normal” 1/4″ seam.

1. Cut your squares 1″ larger than what you need it to be in it’s finished state.  For example, if a quilt has 2″ finished HST in it, they must be made from 3″ squares.
   
2. Make sure that all of your squares are perfectly square.
   
3. You need an equal number of squares from each of two colors.
   
4. For every two squares (one pair) that you sew, it makes two HST.
   
5. To find the number of squares needed, take the total number of HST needed for the entire quilt and divide by 2.  For example, if a quilt is going to have 22 red/blue 3″ finished HST, then you would need 11 (22 divided by 2) red squares and 11 blue squares, each 4″ square.  Why 4″?   Because the finished size is 3″, so add an inch (as given in step 2 above).
   
6. Place the squares into two piles, separated by color.  Refer to this example:

7. On the wrong sides of one of fabrics, draw a diagonal line from one corner to the opposite corner. Use a pencil if it shows up; if not, use a pen. This is going to be in the seam allowance and will not show. It is important to note that you don’t have to draw diagonal lines on ALL of the squares, only on one of the two piles. So, only on half of them. Refer to this example to see where to draw the diagonal line (which is a black line in the illustration. Although I drew it on the right side of the fabric in the illustration, you draw it on the WRONG side.):

8. Pick up one of each colored square, and put the right sides of the fabric together (even though it doesn’t show that way in the illustration!).  Place the square with the drawn diagonal line on top.  Refer to this example (It is important to note that the squares are offset a little just to show how they should be; yours should be evenly aligned):

9. Sew a scant ¼” away from the left side of the drawn diagonal line.  Refer to this example to see where the sewing line (white) is:

10. Turn the squares around and sew a scant ¼” away from the other side of the drawn diagonal line.  Refer to this example to see where the sewing line (white) is:

11. Carefully cut the sewn pair apart ON the diagonal line, not on the lines you just stitched. This makes two HST for each sewn pair sewn.  Refer to the example:

12. Unfold the two HST, and press the seam on one of them to the darkest fabric and press the seam on the other one in the opposite direction.   Refer to the examples:

13. Square up your HST to the size needed (which should be 1″ less than what you started these squares as in the first step), using a rotary cutter (be careful!) and an acrylic ruler.
    
14. Make as many as you need! You have now learned how to make half-square triangles in quilting.

 To make Quarter-Square Triangles in Quilting (QST), follow these simple instructions:

1. Using 2 HST, lay them so that they face opposite directions, as shown:

2. Take the first one on the left and place it face down on the second one. Right sides should be together. Snug them together and pin.

3. Draw a diagonal line with a pencil going in the opposite direction of the seams. You only need to do this on one side.

4. Sew a scant 1/4″ on both sides of the drawn diagonal line.

5. Cut the sewn unit in half, on the drawn diagonal line. This yields two quarter-square triangles (QST) that look similar to this:

Trim these by squaring them up and then press flat.

What is a half-quarter square triangle, commonly known as HQST? It’s a unit made up of three triangles, with one of them being twice as large as the other two.

 Follow these simple directions to make a HQST:

1. Use 1 HST and 1 Solid square, such as these:

2. Draw a line on the wrong side of the solid one, diagonally.

3. Lay them right sides together, sew a scant 1/4″ on both sides of the drawn diagonal line.

4. Cut them apart on the diagonal line. It yields two HQST that look similar to this:

Trim these by squaring them up and then press flat.

Below I’ve attached a half square triangles video from YouTube, showing the same technique on how to make half-square triangles in quilting.

Now that you’ve learned how to make half-square triangles in quilting, you might ask what this can be used for. Well, the opportunities are almost endless, as these can be used in a wide variety of quilts.

On Pinterest there’s a whole section dedicated to half-square triangles in quilting ideas, so I recommend you start looking there if you need some inspiration.