Triangle Fourplay – An Easy Quilt Block of the Month – Block 1

Block 1 of my personal quilt block of the month project

Quilt Block of the month - block 1

Last Updated on 09/28/21 by Rose Palmer

With so much time on my hands, I have decided that each month I am going to challenge my creative grey cells and start my own personal quilt block of the month design. I have been fascinated by half-square triangle quilt patterns for a long time – the number of possible geometries seems infinite. Join me for the next 12 months as I play with half square triangles and figure out which pattern I will make each month. At the end, I will put all the blocks together into a whole new quilt design (or maybe two or three).

A half square triangle is one of quilting’s easiest blocks. Take two right triangles of contrasting fabrics and sew them together, and voila, you have a square (hence, the name half square triangle, or HST for short). Sew 4 of these half square triangles blocks into a bigger square block unit and there are now very many geometric options of how to combine these together.

In fact, there are 4 x 4 x 4 x 4 or 256 total mathematical combinations for putting together these four HST. No, I was not the first to discover this. In fact, a French priest named Sebastien Truchet first started delving into the design and mathematical possibilities of a half square triangle back in 1704 (though he did not call it a half square triangle because he was not a quilter). His work was published by another French priest, Dominique Douat, in 1722 along with a more detailed mathematical analysis that showed how the 256 possibilities were derived. (If you are really curious you can buy a copy of the original treatise in French here.)

However, from a quilting design perspective, many of those 256 mathematical possibilities are actually geometric repeats. So how many unique design possibilities are there when you combine 4 HST? 17. Yes, I did draw out all 256 possible options (I really am that much of a geek) and reduced them down to 17 unique geometries.

3 of the 17 unique geometries possible when you combine 4 HST

Now, if you take one of these 4-HST units and make 4 of them and then combine them together so that you have a total of 16 HST blocks, the possibilities do indeed multiply and seem endless. (Actually, they are not endless, there are 256 combinations again). I will be playing with a different 4 block HST geometry each month, analyzing the many design possibilities, and then sewing together one or two of the patterns that appeal to me.

Triangle Fourplay

I call this first block “sawtooth”.  It is made up of 4 HST all oriented in the same direction. Combine 4 of these 4-HST units together to get a 16 square block “sawtooth”.

Using a quilting design computer program, I started playing around with the orientation of the four 4-HST units within the 16 square block. Since as quilters and designers we tend to prefer symmetry in our patterns, I focused only on producing designs that have some level of symmetry within the block.

I also looked at “positive” and “negative” versions of the same block design. Even though geometrically the pattern is the same, the orientation of the light and the dark triangles can produce a totally different look to the quilt block.

Positive and negative versions of the same block

In the figure below, I am showing the various symmetric 16 block designs that I came up with using the “sawtooth” four-block 4-HST units. There are probably some geometries I may have missed, but still, this is quite a few design options to choose from.

I auditioned each of these possibilities using my sewn 4-HST units.

Quilt Block of the Month – Block 1

Out of all those options, here is the block I chose to sew for this month. I decided to make it in both the “positive” and “negative” variations so that you can see how different they look. For this series of blocks, I am using the Insignia collection of solids by Allison Glass for Andover Fabrics.


Of course, you can use more than just two colors. With three colors, the design possibilities increase even more. I have always wanted to make a red and cream quilt so now I am using this project to get that done.

There is no reason why this block can’t have a scrappy look, so I also sewed a version using some of my leftover Kaffe Fasset fabrics. This version also looks different.

If you want to try making one of these quilt blocks and take part in this Block of the Month party with me, here are the fabric requirements if using a 3 inch HST finished block size.

Fabric Requirements:

For each 12 inch finished block using two colors:

  • Fat eighth or 1/8 yd of two contrasting colors, OR
  • Enough fabric to cut 8 x 4 inch squares of each fabric color

For a quilt with twelve 12 inch blocks I am thinking I will need:

  • 2.5 yards of each of two contrasting fabrics for the 12 blocks
  • 3/4 yard fabric for sashing
  • 1/3 to 1/2 yard for each border
  • 1/2 yard for binding

OR, just use up what you have in your stash and be spontaneous.

Be sure to check out the rest of the blocks in this quilt block of the month series:

Block 2, Block 3, Block 4, Block 5Block 6

Sewing the half square triangle blocks

There are many methods for sewing a half square triangle and I have tried most of them. I am going to share the technique that works best for me.

1. I cut a square 1 inch bigger than the size of the finished HST unit. In this quilt, I want the finished HST block to be 3 inches, so I start with a 4 inch square.

For this block, cut 8 x 4 inch squares from two contrasting fabrics. Using a fat eighth piece of fabric I fold the fabric in half lengthwise and cut two 4 inch wide strips. Then I cut each strip to give me two 4 inch squares. This way I get a total of eight 4 inch squares of each color.

2. Cut each square in half diagonally from one corner to the opposite corner. You will now have 16 right triangles for each color of fabric.

3. Combine two triangles of the contrasting colors with right sides together and sew using a 1/4 inch seam.

4. Iron the seams open.

5. Trim the HST block to the nearest half inch. In this case I trimmed each HST block to 3.5 inches square. You now have a perfectly square HST block that is exactly the size you need.

6. Repeat till you have 16 HST blocks. Chain piecing to sew all the triangles together will get them done more quickly.

7. Sew four blocks together into a 4-HST unit. Do this four times.

8. Sew the four 4-HST units together into the geometry of your choice. The finished block size will be 12.5 inches (12 inches in the finished quilt).


You do not have to make this design using 3 inch finished HST blocks. You can make it as big or as small as you like. Use the table below to figure out what size square you need to cut for the finished HST block size you want to make.


I have made a number of quilts using different half square triangle designs. Check out the “Not Your Grandfatehr’s Herringbone” quilt or the “California Dreamin” quilt, among others,  in my Quilt Gallery for inspiration.

I hope you join me each month for this quilt block of the month challenge and play along with me. Come back to see what I put together next time. A new post with a new block design will go up on the website toward the end of each month.

See you next month and thanks for visiting.



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Join me for a block of the month using half square trianglesBlock 1 of my easy block of the month quilting challenge