Tuesday, June 13, 2017

Beginners Unite! Half Square Triangles

This is the post I have been waiting for since the beginning. I love making half square triangles, as long as they are "perfect."

There are a ton of different ways to make the half square triangle unit, but this is the only way I have found, for me, that gives me a perfectly squared HST (half square triangle). A perfectly squared HST goes a long way towards making the unit enjoyable. There is nothing worse than a unit that doesn't fit into a block, or a unit where you lose the point. 

We're going to make two 2 1/2" unfinished HST unit. For this you will need:
1) Two squares, 3" each 
See this post for accurate cutting.
2) A marking tool, I prefer a mechanical pencil
3) A ruler with a 45° line
*Any ruler will do, I love my Tucker Trimmer (no affiliation)
4) Rotary Cutter

On the wrong side of the lightest fabric draw a diagonal line.

At your sewing machine we are going to sew a scant 1/4" on each side of the fabric. To sew a scant 1/4" seam for a HST, I line up my foot so the marked line is under it, not next to it.

Turn the square and repeat on the other side of the line.

Cut directly on the line.

Press to set the seam. 

Then press towards the dark fabric.

Now, the fun part! Squaring up.

I have a piece of old cutting mat that I use when I do any squaring up. Our mats do wear out, but they are expensive and I can't bear to throw mine out. So my last one I cut/broke into quadrants and I use them any time I need to trim units. This keeps the mat I'm using as fresh and long lasting as possible. If you don't have an extra piece of mat, flip your mat over and use the back side for trimming.

I will show how to trim using the Tucker Trimmer as well as a square Creative Grids ruler.

What I like about the Tucker Trimmer is how it has just the lines you need, nothing extra. It makes trimming much faster. I will say, I wish it had grips like Creative Grids, be careful that the ruler doesn't slip. 

Line up the diagonal along the seam of your HST. This first trim is going to be taking off as little fabric as possible.

We made the square larger than needed, so there should be plenty to trim off, but double check that the measurement you need is inside the fabric. In this case the 2 1/2" mark.

Rotate the HST. Now you want to line up the 2 1/2" mark along the edge of the fabric, lining up the diagonal line on the seam. This trim will have larger pieces. 

You now have a perfect HST.

Using a Creative Grids ruler, you do the same thing. Line up the first trim with as little fabric showing as possible. The diagonal line sits on the seam and the 2 1/2" mark (for this size). 

Rotate the HST, and line up the ruler with the 2 1/2" mark along the fabric. Trim.

Half Square Triangles are an easy unit to chain piece. You can make a lot of them in a short amount of time, and it's worth the time to trim them into perfection.

If you don't like to draw any lines on your fabric, you can use this trick: Draw (or tape) the lines directly on your machine and line up your squares on them. 

I mentioned above that there are a lot of ways to make HSTs, and there are other rulers made just for squaring them up. Please feel free to share your favorite way/ruler for making the perfect half square triangle in the comments.

Happy Stitching!

1) Intro - May 2
6) Sewing strips and squares - June 6
7) HST - Half Square Triangles (My one true love) - You are here
8) Flying Geese - June 20
12) Adding Borders - July 18
13) Sandwich that top - July 25
14) Quilting - August 1
15) Binding - August 8
16) Labels  - August 15


  1. Jen, I love a good tutorial and really enjoy this series. Lovely!

    1. I'm so glad, Sandy! Thank you for taking the time to share that. Makes my day. :)

  2. Hi Jen. Thank you so much for this tutorial and for the muggamo series. I am using both to develop my skills. It is such a relief to work on a small project like the mug rug and hopefully perfect the techniques before I start something larger. Have completed January and February and looking forward to working on March today! Your directions are wonderful and the patterns are just lovely. Thanks again!! Linda B


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