Thursday, May 9, 2013

How-To Square Up Half Square Triangles

Most of my friends are not quilters but recently one of them decided to make a quilt for a family member.  She chose two fabrics (grey and white solids) and began to make lots of half square triangles (HST's).  She planned to put them together to create a simple, modern chevron quilt.  After she made all of the HST's she started to sew them together in rows.  Everything seemed to be going great until she started to sew the rows together.  Then, she called me in frustration.  We met up and she showed me how the intersections of the HST's were not matching up, her points were either getting cut off or weren't lining up and some blocks seemed to be bigger than others.  She had pulled, pushed and tucked to try to make them all fit but it just wasn't working!  I could see she was very frustrated and discouraged.  We checked her seam allowances and tried to figure out the root of the problem.  While trying to stay positive and remind her that "finished is better than perfection" I could tell she wouldn't be happy until she unpicked her rows and squared up her blocks.  That was the only, yet critical step, she had missed.  So I told her how to square them up and she went home.  She called me a couple days later asking if we could meet up so I could show her (again) how to do it.
For a newbie quilter like my friend, using rulers for cutting and squaring up can be confusing.  I work in a quilt shop and I see how intimidated people get by it.  Sometimes they'll even bring their blocks in and ask us to square up their blocks for them! :)  

But it really is necessary to take the time to square up.  Squaring up can help you straighten up (so your diagonal seam goes exactly from corner to corner) and it can help you to size up!  Your quilt blocks will be so much easier to put together if they're all the exact same size!  It will take a little extra time but squaring up is totally worth it in the end!

Then I got thinking, there are probably others out there that struggle with the same thing as my friend.  So I've decided to do a little "How-To" on squaring up HST's.  Of course, there are several ways to do it.  This is just the method I like.  Let's begin, shall we?

 First, you'll need a self-healing cutting mat, a rotary cutter and a small ruler that is at least the size of what you want your trimmed size block to be.  I am not one to have a million different size rulers but I've found that my 6 1/2" square ruler works well for most projects.

Decide what size you want to trim all of your blocks to.  As you can see in the above photograph, my HST was about 3 5/8".  I wanted to trim it to an even 3 1/2".  So that doesn't give me much room to square up (only an 1/8").  I only need to trim off a sliver of fabric from each side.

Note: You don't need to pay any attention to the grid marks on your mat.  We're strictly using it as a medium to cut on.  Only pay attention to the marks on the ruler. 

Step 1: Line up the top and right edges of your ruler on the HST.  Make sure your 45 degree line on the ruler is directly over the seam.  You will be trimming both of those two sides first but make sure that the other two sides extend beyond your desired trimmed size (3 1/2" for this example).  If they do not extend beyond the 3 1/2" mark then you will have trimmed off too much and your block will be too small.

 Go ahead and trim the first two sides when you're sure you have the right ruler placement.  Be careful that nothing slips while you're cutting.

Step 2: Rotate the block 180 degrees to the left so that you can trim the other two sides in the same exact way.  This time you can line up the two trimmed sides on your 3 1/2" marks on your ruler.  Also make sure that the 45 degree line on your ruler is directly over the seam.  When everything is straight and lined up, trim off the top and right sides.

Your block should measure exactly 3 1/2" (or whatever you chose to trim yours to).  The dog ears will be cut off and your seam will be a perfect 45 degree line from corner to corner!

That's it.  It's really quite easy peasy.

I think you'll find that although it takes a little extra time to square up...

it's totally worth it and will save you from lots of headaches in the future.

I hope that helps!

Happy quilting!
~ Amber


  1. Thank you for the excellent tutorial. So easy to follow!

  2. Even knowing how to do it,I found that a brilliant tutorial!!

  3. And if you want to make the whole process even easier, check out a square ruler product called Bloc-Loc. It's designed to catch the seam in a groove in the bottom of the ruler to straighten the seam and lock it in place while you trim. It's amazing. I got mine at a quilt show and LOVE it! They also have them for Flying Geese.

  4. I actually bought a special ruler by June Tailor...course it only does 1/2", so that could be a problem...but I'm using it now for my 4 1/2" squares and love it.

    Thanks for your tutorial though...if you don't have that ruler, this is definitely helpful!

  5. Thank you for taking the time to post such a useful tutorial...appreciate all the pictures too!

  6. What a great tutorial! I love squaring up too. It is kinda therapeutic. :) And boy does it cut down on the stress later when everything matches up perfect.

  7. Thank you. This is very helpful I have been doing it wrong all along.

  8. Your tut is excellent and will make a difference for any HST lover wannabe. It is a critical step and you explained it well (aka, just how I do it...:) Ha!
    FYI: 18 months ago I converted to pressing my seams open; but before when I would press to one side, I loved my BlocLoc ruler.

  9. Very good tutorial and everyone can use a little reminder from time to time. You are so right about squaring up being important.

  10. Very Nice Amber! Back in the day, we never squared up but it makes things SO much easier and more accurate!

  11. Thanks for sharing... so very easy to follow...Do you square up a block that is not hst the same way? Maybe that really is not a question.......mmm really like your blog..

  12. Thank you! I'm working on HST right now and I needed this reminder.

  13. I'm so glad to have found your blog. Your work is so lovely *
    I'm learning patchwork and this tutorial is a great help for me.
    Thanks so much Amber

  14. Thanks so much for this tutorial ...I have been quilting for a long time and never understood how important this is!

  15. Thanks for this great tutorial! It is such an important step, although not too exciting to do.

  16. Thank you so much for making this clear----I wasn't squaring up correctly! How silly! I didn't even "see" the diagonal line on my ruler, oh my goodness..... My chevron quilt was off just like your friends, so I unpicked it, and now will square up the right way. Thanks so much for taking the time to post this. :D

  17. Hungryhippie,

    So glad I could help! That makes me happy :) Thanks for letting me know and good luck on your chevron quilt!


  18. Your tutorial was very well presented. Can you use this method to square up quarter square triangles also? Thanks again for the tutorial!

  19. Great tutorial, very helpful.


I ♥ to hear from you so please feel free to leave a comment. I read each one and try to respond as often as I can. Thanks so much for stopping by! ~Amber