Squaring up Half-Square Triangles

It has been so fun to already see blocks popping up in the Virtual Quilting Bee Flickr group. One of my favorite things about quilting is seeing the variety of colors and fabric choices people use. 
I’ve decided to make my own version and spent the morning pulling fabrics from my stash in a new palette I’ve never tried. It’s a bit of a break-away from my traditional primary-color palette that I use most often. I’m kind of excited. Most of the fabrics are bits and pieces from favorite fabric collections from days of yore like Denyse Schmidt’s Hope Valley, and a few of her collections from JoAnn’s, Joel Dewberry’s Deer Valley plus I’ve thrown in a bunch of the recent Bike Path Dots by Alison Glass that I’ve been itching to create with.  I’m excite to play with this stack. 
When making my block, I remembered that a couple of people have asked me for a quick tutorial on squaring up half-square triangles. So here’s a quick explanation: Half-square triangle (HST) blocks are one of the most versatile blocks in quilt-making. They are quick and easy to make as Sherri showed by drawing a diagonal line on the back of one of the squares, matching the two prints right-sides together, and then sewing down either side of the line with a scant 1/4″ seam allowance.
Then cut on the drawn diagonal line and press both blocks open and voila: two identical half-square triangle blocks! As Sherri mentioned in her tutorial, you are going to want to square-up these particular HST to 2 1/2 inches – that means trim them to the right size and make the sides straight – or “square”.  I personally like making my HST’s slightly large and squaring- up the block when I’m done because it makes the blocks so much neater to work with.
Even with the most careful of sewing, when you sew on the diagonal you are sewing on the bias. Drawing that line and sewing before you cut, will help keep the diagonal edges from stretching but there will still be some misshapen edges on those blocks. Squaring-up will make things nice and neat, not to mention the right size, in many cases. 

One of my favorite tools for squaring up HST blocks is a square ruler with a diagonal line. (There are lots of nifty tools for such purposes.) You don’t need to have this – it’s definitely possible to square-up with any ruler – but if your quilting budget allows for one of these, over time it’s a great investment.

When squaring-up a pieced block, you want to be careful to keep that diagonal seam running from corner to corner. If your ruler has a diagonal line on it place that line right over the seam. This will keep your seam centered and your block square. If your ruler does not have the diagonal line, place the corner point of the ruler over the seam and make sure the point you are measuring to (in this case the 2 1/2″ point) also on the diagonal seam at the other end.

First trim two sides, then rotate the ruler so that the 2 1/2″ lines (in this case) are on the newly squared-up edges and square-off the other two edges. I know it’s a little more tedious to square off all 4 sides, but it definitely makes that block neat with straight edges on all four sides.

If the block has fairly square sides before sewing up, you could place the 2 1/2″ lines directly on the left and bottom edges (right and bottom if you’re left handed) and just square-off the right and top edges. Your call. Make sure you trim those little ‘tags’ in the corner though, so you won’t have a lot of bulk when assembling your block.

Post Edit: I have since found a new favorite short-cut method for squaring-up HST’s using a specialty ruler.

Hope that helps!

And just a reminder – I’m answering questions as much as possible in the comment sections of each post.  Let me know if I’ve missed something. Thanks again for playing along!

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  • Reply
    March 11, 2013 at 4:39 pm

    amy this is an awesome post! I just finished trimming a boat load of HST&#39;s last night! I wondered how everyone else did it, and I&#39;m also glad to know that everyone&#39;s edges are sometimes a little wonky … good point that you&#39;re sewing on the bias when you go from corner to corner. <br /><br />

  • Reply
    linda f
    March 11, 2013 at 5:22 pm

    Amy,<br /><br />Thank you so much for a wonderful post. I am enjoying the viirtual quilting bee.<br /><br /><br />Have a great night.<br /><br />Linda

  • Reply
    Chris S
    March 11, 2013 at 6:35 pm

    Thanks! I&#39;m fairly new to all this and these little tips help so much!!

  • Reply
    March 11, 2013 at 6:49 pm

    Amy!!! Thank you so much for this tutorial! I am going to give this a try and see if I can make some HST&#39;s that are not wonky!! You are terrific!! 🙂

  • Reply
    March 11, 2013 at 8:24 pm

    That&#39;s a pretty palette! Love how the block turned out.

  • Reply
    March 11, 2013 at 9:56 pm

    Thanks for the reminder, I often forget to use all of the lines on my quilting rulers!! Cathyx

  • Reply
    March 12, 2013 at 5:04 am

    I absolutely love the color palate of this block! I cannot wait to see the final quilt!

  • Reply
    March 12, 2013 at 7:17 am

    Thank You!

  • Reply
    March 12, 2013 at 8:13 am

    Very cool Amy — I LOVE your version of the block!

  • Reply
    March 12, 2013 at 9:31 am

    Great information, but a quick question. When you say you make your HST&#39;s slightly larger, do you add 1/4&quot; to the sides of the squares? 1/2&quot;?

  • Reply
    Three Sisterz
    March 12, 2013 at 1:28 pm

    What a great fabric collection!!! Please come to Philly and help me to pull mine together!!!<br /><br /><br /><br /><br />Courtenay<br /><br />p.s. Great explanation of &#39;squaring up&#39; these triangles.

  • Reply
    Katy Cameron
    March 12, 2013 at 2:00 pm

    Love those fabrics you pulled, and I&#39;m a huge CG ruler fan!

  • Reply
    Reese @ Quilty Reese
    March 13, 2013 at 6:58 am

    Have you ever tried the Bloc-loc ruler? I love it. I am not sure how it would work though if you press your seams open.

    • Reply
      amy smart
      March 15, 2013 at 1:34 pm

      I&#39;ve never tried them – I just googled them and they look cool. Has anyone else tried them?

    • Reply
      January 13, 2014 at 12:02 am

      I just tried my Bloc-loc ruler for the first time. I love it, but the down side is that I you can only use it for seams that are pressed to the side, not open.<br />Thanks for a great post, Amy!

    • Reply
      January 13, 2014 at 12:02 am

      This comment has been removed by the author.

  • Reply
    Rach H @ FamilyEverAfter
    March 14, 2013 at 11:05 pm

    Amy, this might be a dumb question, but I&#39;ve always wondered, so I might as well ask :)<br /><br />When you square up the blocks, are you trimming away your backstitching? Should you backstitch a little more that usual so as not to trim so much off? Or, if you are trimming it, is it not a big deal since the blocks will be sewn to another square anyway?<br /><br />If you have time to answer,

    • Reply
      amy smart
      March 15, 2013 at 1:32 pm

      Great question, Rachel! I generally don&#39;t backstitch at all when I&#39;m piecing. (The only exception is when I am sewing Y-seams, such as when I machine-piece hexagons.)<br /><br />Other than that, you don&#39;t need to. As you said, the seams and blocks intersect so much, that they stay stable. Saves a lot of time too and makes it much easier to chain stitch (sew pieces together one after

  • Reply
    Christina Mejer
    March 30, 2014 at 7:09 am

    Thanks for the great explanation on how to use this ruler! Creative Grids rulers have tutorials for all of their products on their web site, too.

  • Reply
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  • Reply
    Melissa Boyd
    February 13, 2016 at 8:28 am

    I’m a new quilter and this is the first time I’ve understood HST and squaring them up. Thanks so much.

  • Reply
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