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My Top tips for perfect HSTs

HSTs (or Half Square Triangles) are one of my favourite blocks and I use them a lot in my patterns in particular ‘My HST Quilt’.

HST quilt WIP

There are many different ways to make HST blocks. My preferred method is the one that yields 2 HSTs by drawing a line down the centre and sewing a seam either side of that line. (Most patterns will give you instructions on how to make the HST block.)

Getting the perfect HST can be tricky sometimes though, so I have complied a list of my top tips to help you find some confidence and enjoyment with these fun little blocks.

(There are a few Affiliate links in this blog post – they will be the links highlighted in pink and bold, like this. if you click on the link and purchase something, I‘ll get a little commission, which helps me run my business, so thank you!)

Tips for the perfect HST quilt block


Let’s get to it!


Accurate sewing

Just because you are going to trim it later, it doesn’t mean you don’t have to be accurate when sewing the first step.

An important part of getting the perfect HST square is a 45°angle on the seam and that starts with the first stitch. Make sure that the line you draw is a 45°angle going from corner to corner of the square, then make sure that the lines you sew either side of this is as ‘straight’ as you can make it.  

If you are following a different method to make HSTs, then make sure that line is straight too!



Press and starch it

You’ve got your accurately sewn HST block and now you need to press it. Set the seam first by pressing it while it’s still closed up, then starch.

A spray of starch before you press it open helps create a crisp HST block (which will make the next steps easier.)

My personal favourite is Mary Ellen’s Best Press. I’ve tried a few different starch/pressing sprays and for me, this gives the best results. It comes in lots of different scents, or unscented, personally I prefer Linen or Unscented.


The last tip when pressing is to be careful not to distort/drag the fabric, remember we want to keep that seam at a 45°angle! (It may be a bit of a faff but to carefully finger press the seam back first and then press that into place can help.)


Sharp trimming

It’s trimming time. In my patterns, I like to give a little wiggle room for trimming, because a well trimmed HST can make all the difference. We are back with that 45°angle again. You need to make sure when trimming that the seam runs at a 45°angle into to each corner.

Two things can help with this, one, firstly, a sharp blade, so that you cleanly cut the fabric and don’t drag/ distort whilst cutting. (Careful for your fingers!)  

Second, is a Bloc Loc HST ruler. This cutting square has a little gap running through it, which allows it to nestle over the seam so that the ruler can lie completely flat on top of the block. This helps with accurately cutting. (I have a 4 ½” square one which means I can trim to 4 ½” and under, which covers most HST blocks I make.)

Trimming HST with Bloc Loc ruler

A little bonus tip is a rotating cutting mat – it might not make it more accurate but it will make it quicker. Trim one side, spin the mat and trim the other, the HST block doesn’t have to move!


Seam allowance

The industry standard for quilting is 1/4” seam allowance. For increased accuracy, I would recommend a scant seam allowance (more on that another day) but the main thing when sewing patchwork is that you keep your seam allowance the same for all seams. This last part will mean you keep our dear friend, the 45°angle seam line.



Are you now raring to go with a new found love for HST blocks? If so, I have a number of patterns that have HST blocks at the heart of the design.

The literally named, ‘My HST quilt’ and ‘Charmed’ are brilliant examples of how the HST block can be used to create many different designs and patterns with both the print and negative space.  

My HST quilt patternCharmed quilt pattern

I hope you find the tips useful and have found a new little nugget in there to help you increase your confidence when sewing. Please remember to try not to worry too much about getting your patchwork exactly perfect though.

It’s handmade and any slight ‘imperfections’ here and there make it unique.  


cutting matbloc loc ruler


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