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How to Trim Half Square Triangles with a Basic Ruler + GIVEAWAY ANNOUNCEMENT

Today’s post is part of a series of video tutorials showing you how to use some of my favorite rulers.

Find more ruler tutorials here.



If you have purchased my quilt patterns in the past you know I love my Quilt in a Day Square up Ruler for trimming half square triangles. I SWEAR by this ruler. I have a tutorial for it right here and when I use this ruler all of my HSTs are about as perfect as I’m capable of getting them.

They make the standard up to 6.5″ size here, but they also have a up to 9.5″ size ruler as well. The 9.5″ version can do everything the 6.5 version can, plus bigger HSTs.

Today though, I’m showing you how to make HSTs when you DO NOT have a specialty ruler. In the video, I’m showing you how to make them with a basic 12.5″ square ruler, but know that you can make them on just about any ruler. All you need is washi tape.

Scroll to the bottom for giveaway details!


Everything You Need for Perfect Half Square Triangles

Here’s my magic formula ritual:





We’ve got a lot to cover today, so I’m diving in and getting to it quickly.  No funny business!

Let’s go over some quick “you should know” things first.

  1. Decide what size your HST should be finished.  Let’s say that I want it to be 4″
  2. I need a trim-to size.  I need seam allowance.  This means my unfinished HST needs to be 4.5″
  3. If I’m trimming this guy to 4.5″, I can’t start with that size, I need seam allowance again.  So you add another .5″ to that and your starting square size is 5″.
  4. This method of making HSTs makes 2 of them at a time.

Back to the math… If I need an unfinished 6.5″ HST, that means I need to start with 7″ squares.  If I need a 2.5″ unfinished HST, that means I need to start with 3″ squares.  You get it!

Finished means it’s sewn all up into a quilt.  Unfinished means we haven’t sewn them together yet, they are a unit or a block.  Still with me?

If you are very lost here and think you might need a more detailed lesson about seam allowance, here’s a class that might help.


Product Spotlight

Diagonal Seam Tape

Diagonal Seam Tape is a perfect solution for sewing straight diagonal seams without having to mark any lines!

Get yours here.



Avoiding that jankiness

Let me just get this out of the way and tell you that obviously my method is NOT the only method.  There are lots of lovely methods and you should find the one that you like the best.

Anytime you cut a fabric into a triangle, you’ve made it stretchy, you’ve made it vulnerable.  Vulnerable to ALL THE THINGS!  I like to call them the precious little babies, because that’s how you are going to have to treat them if you want them to act right and stay in place and stay not-janky.

Here’s a list of things NOT to do:

  1. Don’t stretch them.
  2. Don’t iron them, press instead.  PRESS.
  3. Don’t tug at them.
  4. And for goodness sake, use your starch.  It is your bestest friend when making patchwork.




The washi tape is just to help you see the lines a bit easier. It’s not a requirement, but it really is helpful in my opinion. Also, when sewing on both sides of the line, remember to sew with a SCANT 1/4″ seam or they won’t come to size.

Products used in video:


My Quilt Patterns


Shop All Patterns Here



Pop over to my latest Instagram post (posted today 10/23/20) and enter the giveaway. Havel’s has kindly agreed to give a 12.5 and the 6.5″ square rulers to two of my readers. You’ll need to like the picture and tag a friend, and be following myself and Havel’s Sewing to be eligible to win. Good luck!!



Product Spotlight

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  • 10 pieces
  • Fat quarters
  • Extra yummy
Get your bundle here.




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