square up your half square triangle quilt block | patchwork posse | easy sewing projects
Quilt Blocks Becky  

How to Square Up A Half Square Triangle Quilt Block

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So, you have sewn a bunch of half square triangles…..and now’s the fun part.  Or not!  Squaring up.  This is a totally important and actually crucial part of quilting. If you end up not squaring up your quilt blocks, they will haunt you for ever more in the quilt!

square up your half square triangle quilt block | patchwork posse | easy sewing projects

The quilt blocks won’t line up.  They will get all distorted and by the time you sew them together and add a few borders you are done for.  Everything is off.  The seams won’t match, sometimes the top of the quilt is bigger or smaller then the bottom of the quilt.  It all goes crazy- crazy.

To avoid all the frustration and issues, it’s time to learn how to take the time to square up your quilt blocks.

The most offensive is the half square triangles.  They tend to never be right after you cut and sew.    I would recommend making your half square triangle a titch larger than you really need so you can trim it to the correct size.

You’ll be so much happier in the end!



Bloc Loc Ruler  – method #1

Quilting Ruler – method #2

Supplies you may need:

Square Up half square triangles- #1

Use the Bloc Loc ruler.  This ruler is super fancy.  It has a diagonal trench on the wrong side of the fabric.  The seam area of your half square triangle quilt block will nestle in the trench.  *if it doesn’t, adjust where you are placing the ruler until it does.

Move the ruler to the correct size of block– the one I was going for was 3 1/2″ X 3 1/2″   Remember that at each corner, there should be your center seam.  They should be at a point.  If they aren’t you will need to adjust where you are lining the ruler.

square up your half square triangle quilt block | patchwork posse | easy sewing projects

Square Up half square triangles- #2

Use a regular ruler.  Method one– the quilt block is closed.

Watch this…..you can cut your half square triangle BEFORE you iron it open.  How awesome is that!

1)  Take your dry erase marker and connect the same measurement on one side and on the other side of the ruler.    Draw this line with a dry erase marker….you will use this drawn line as a guide in the next step.  If you accidentally mark an incorrect line wipe off and start again.

* the measurement you are using to draw the line on is what you want the half square triangle unfinished size is.   So, for instance if the quilt pattern called for 2 1/2″ half square triangles, you would mark a line from 2 1/2″ to 2 1/2″.


3)  Line up your CLOSED half square triangle with the drawn line and trim the sides.  The drawn line should be on top of your seam for the block!  You can’t see my drawn line below, but I highlighted it with the white dotted line.  See how it lines up with the seam of the block.


Method 3:  still using a traditional ruler–

1)  Open the half square triangle and iron

2)  Line up your traditional ruler similar to the bloc loc, the diagonal seam is lined up with the corner of the quilt block.

3)  Trim the sides

These techniques work great when you have a bunch of half square triangles to sew and cut.

It’s one of the worst things about quilting for me…. I am not one to have patience with this step, but have had HORRIBLE luck when I skip it.

I would suggest you take the time to do it.  You’re life will be so much better!

Do you have a trick when it comes to squaring up your half square triangles?


6 thoughts on “How to Square Up A Half Square Triangle Quilt Block

  1. Carol Stearns

    I like to use the easy angle ruler to cut HST as described by Bonnie Hunter on her blog. I usually press open and then cut but using this ruler helps to eliminate much of the trimming up. The next time I do this, I will see about trimming up before pressing open, putting the angle of the ruler on the seam. Seams sometimes get wonky as you sew creating non squares. Thanks for the tip.

  2. Becky

    Carol- thanks for your tip. Good luck with the new method too!

  3. Allie

    This is awesome – I have such a hard time with hst’s and now I know why. I’m going to do this next time. I’ve been wanting to make a whole quilt with nothing but hst’s, if I ever get time to quilt again lol, I will give this a try. Thanks!

  4. Susan

    And the other advantage is that it gets rid of all those annoying ears that will also throw your block out of whack! I just use my diagonal line on my square ruler and it works like a charm, though I like the idea of those Blok-Loc rulers and next time I need a new square ruler, I’m going to try one. Saw you linked on Allie-Oops blog.

  5. Jean

    Very helpful. Wish I had found this ‘how-to’ before I cut 40 HST incorrectly and found that nothing lined up as it should!! Back to the cutting mat for me!

  6. Glenda Constable

    What a neat and helpful way to square HST. I tried this second method and love the results. Wish I had found this out sooner. Thanks so much for your helpful post.

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