Block Basics: Half-Square Triangles – 4 at a Time

Today we’re going to be talking about 4 at a time Half Square Triangles (HST).

These you have to be careful with because they’re cut on the biased and will stretch in weird ways. So just be careful when you’re pressing them and sewing them.

How to Make 4-at-a-Time Half-Square Triangles

Cut List

  • 5 1/2” Square Background fabric
  • 5 1/2” Square Main fabric

Place fabrics together right side together.

Sew a 1/4” seam all the way around each edge. Seams will create a square.

Take your sewn square to the cutting mat and cut the square on the diagonal from corner to corner, twice. Cut lines will form an X on the square.

Press open toward the dark or main fabric. And you have 4 Half-Square Triangles.

Measure and Trim

Trim to 3 1/2” x 3 1/2”. Once again, be very careful when you open these and press, as the blocks might not be square or the diagonal in the middle won’t be straight.


If you have any questions, please go watch the YouTube video. I go into much more detail in the video, and you can watch it and follow along.

If you have questions after that, drop them in my comment section below, or on the comment section of the video and I will come and answer them.

How to Make Any Size Half-Square Triangles

What if you want a different size of your block? It’s time to do some math. We need to figure out what size of starting square you’ll need.

Using the unfinished size half square triangle block you would like (in the above example my unfinished size is 3 1/2″ square) you will take 3 1/2″ and divide it by .64. That will be the starting size square you will need to cut.

I like to round up on this. if you do it by a calculator, you get 5.46875″, so I just rounded up to 5 1/2″ square.

You can figure it out the other way as well. But, I’m not sure how often you would actually use it.

Take the beginning size square you are starting with, say 5 inches, for example, you will multiply by .64 and that will give you the unfinished size block that you will be making. 5 X .64 = 3.2″ Unfinished HST.

Beginner Skill Builder Sampler Quilt

For quilt block 3, we will be putting them into a pinwheel for the center of the block.

In the video above, I put the pinwheel together as part of the 4-at-a-time HST tutorial. I’m going to include it in the steps to making block 3, so go check that out.

Next week you get to learn another way to make Flying Geese. This one’s actually my favorite way. So I’m excited to show it to you.

And Week 3 is tip week. We will be talking about ironing.

Tag me!

I would love to see your progress. Just tag me at #theashleytomlinson or #ashley_sunnymade and I’ll be able to see you on social media. 

I want to see how they turn out!

Happy sewing!