Half-square triangle blocks are one of those quilting basics skills that you'll use forever in your quilting adventures. They show up in everything from classic pinwheels to modern stars (this quilt alone uses 12 HSTs!) With this quick 2-at-a-time method you can stitch up a neat stack in no time. Today I'm walking you through the easiest way to make them and, even more importantly, how to square them up so every block is crisp, accurate, and ready to play nicely with the rest of your quilt.
How to Make HST Blocks Two at a Time
HST are quick and easy to make 2-at-a-time 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 ¼" seam allowance.
Then cut on the drawn diagonal line and press both blocks open and voila: two identical half-square triangle blocks!
Why You Need to Square Up HST Blocks
After sewing the two identical blocks you'll need to "square up" the sides. "Squaring-up means" to 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 45 degree 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.
How to Square Up HST Blocks (Keep the Seam Centered)
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 45 degree 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 ½" point) also on the diagonal seam at the other end.
Trimming Steps: Square All Four Sides
First trim two sides, then rotate the ruler so that the 2 ½" 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 ½" 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: Since writing this post, I have found a new favorite short-cut method for squaring-up HST's using a specialty ruler that will cut your square-up time in half!
SewSara says
amy this is an awesome post! I just finished trimming a boat load of HST's last night! I wondered how everyone else did it, and I'm also glad to know that everyone's edges are sometimes a little wonky ... good point that you're sewing on the bias when you go from corner to corner. <br /><br />
linda f says
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
Chris S says
Thanks! I'm fairly new to all this and these little tips help so much!!
CathyK says
Amy!!! Thank you so much for this tutorial! I am going to give this a try and see if I can make some HST's that are not wonky!! You are terrific!! 🙂
LynCC says
That's a pretty palette! Love how the block turned out.
Cathy says
Thanks for the reminder, I often forget to use all of the lines on my quilting rulers!! Cathyx
robin says
I absolutely love the color palate of this block! I cannot wait to see the final quilt!
contentncm says
Thank You!
Thimbleanna says
Very cool Amy -- I LOVE your version of the block!
Martha says
Great information, but a quick question. When you say you make your HST's slightly larger, do you add 1/4" to the sides of the squares? 1/2"?
Three Sisterz says
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 'squaring up' these triangles.
Katy Cameron says
Love those fabrics you pulled, and I'm a huge CG ruler fan!
Reese @ Quilty Reese says
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.
amy smart says
I've never tried them - I just googled them and they look cool. Has anyone else tried them?
Andrea says
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!
Andrea says
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Rach H @ FamilyEverAfter says
Amy, this might be a dumb question, but I'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,
amy smart says
Great question, Rachel! I generally don't backstitch at all when I'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'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
Christina Mejer says
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.
Melissa Boyd says
I'm a new quilter and this is the first time I've understood HST and squaring them up. Thanks so much.
Amy Smart says
That makes me so glad!
Charlotte says
Thank you for reminding me the best (and quickest) way to use my square up ruler before opening the triangle! Bless you!
Amy Smart says
You're welcome. ☺️