This post was updated in 2019 with additional information and video to make Half Square Triangle quilt blocks quickly and accurately.
I have been making a LOT of half-square-triangle quilt blocks recently. Half-square-triangles (or HST’s) are one of the greatest basic building blocks of traditional quilting. I’m not a super-duper-precise piecer, but I am a firm believer in squaring-up blocks – especially half-square-triangle blocks.
It just makes the piecing come together easier and look so much nicer in the end.
But as we all know, the square-ing up process can get kind of tedious. Right? So I thought I’d share a trick I finally just discovered that has made the work SO much easier and faster. Oh my goodness, I don’t know why this took me so long to figure out. Many of you are probably already doing this, but just in case you’re like me, here’s the scoop:
First of all, this is my favorite basic method for making HST’s: Match two squares right-sides-together and draw a diagonal line down the back of one side. Sew a 1/4″ seam on both sides of the drawn line. Cut on the drawn line. This will create two HST blocks. I generally like to make my blocks slightly larger than the final size so that I can have room to square them up. If you are making a bunch at once – especially if you are chain-piecing them – it’s really easy for seams or matched-up squares to get slightly distorted. Here is the traditional way to square-up a half-square-triangle block.
This Quilt in a Day Square up Ruler* makes the process SO MUCH faster. I’ve seen this ruler multiple times in shops, in my mom’s sewing room, etc. and always wondered what it did, but never bothered to find out. Well I finally did and it’s genius. The ruler is marked from one corner with traditional inch marks divided into eighths. From the opposite corner it’s marked in half-inch lines.
Before you even open the HST block, lay the corner of the ruler on top of the pieced block and match up the marking for the desired finished size of the block, right on the seam. (So for example, I want a 3″ finished block, so I am laying the 3″ line on my seam, NOT the 3″ line on the bottom edge of the triangle.)
Trim two edges using a rotary cutter. By laying the mark on the seam you get a square block with the diagonal seam centered when you open up the block.
I then use my rotary cutter to trim off the ends so that I won’t have the little triangle tags when I open up the block.
And voila – a perfectly squared-up 3″ HST block with no tags sticking out at the ends. Before you open up the block, press along the seam to “set the seam.” Then press the block from the front, careful not to pull or distort the diagonal seam, using the tip of the iron right on the seam to make sure it is fully opened and flat. Makes the blocks so nice and crisp and the best part is that I can get through a stack of them so much more quickly. I suggest doing the whole stack one step at a time. (For example: sew all blocks, trim all blocks, and then press all blocks, to streamline the process.)
I traditionally press my seams to the side – usually the dark. Sometime though I’ll press my seams open, especially if the blocks are small.
Here’s a repeat of the process again, this time making my block a 2 3/4″ block. Notice the arrow in the top left picture where I have lined up the 2 3/4″ markings with the seam. Trim two sides, open and press. (Ruler in bottom right photo only to show finished dimensions.)
I know there are a lot of quilty-gadgets out there, and you don’t need every one, but if you make a lot of HST’s and dislike the squaring-up part, Quilt in a Day Square up Ruler is worth it. (I know they are available also at JoAnn’s and from the Quilt in a Day site.) I now use it ALL the time.
If you’re looking for more half-square-triangle inspiration, here are a few other projects I’ve used them in: Half-Square-Triangle spectrum quilt,
Plus a whole pinboard of Half Square Triangle inspiration!
*FTC Disclosure: this post contains affiliate links. If you purchase something through one of those links I may receive a small commission, so thank you for supporting Diary of a Quilter when you shop! All of the opinions are my own and I only suggest products that I actually use.