How to make half-square triangles 4 at a time

Welcome to the second instalment of my half-square triangle tutorial series. In this tutorial I am going to show you a time-saving method for making four HSTs at once. This method is especially useful when you want to make a quilt with many of the same HSTs, meaning they all use the same fabric combination.

You could make them two at a time as shown in the first instalment of the series, and there's nothing wrong with that. But sometimes it helps to be able to make multiples of the same thing, with a bit less initial cutting and fewer stops at the sewing machine.

This is a method I wish I had learned about a lot earlier. HSTs are such a versatile basic block to have in your quilter's arsenal, and they get used in so many ways that I made many hundreds of HSTs using the 2-at-a-time method and wishing there was a faster way before I learned about this method. So hopefully you're seeing this tutorial earlier in your quilting journey and I can save you some time and cutting.

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Three easy ways to make HSTs

There are three main methods for making half-square triangles, and I am showing you all three in this tutorial series:

• Two at a time - the easiest method and usually the first one new quilters learn. It's perfect for scraps or patterns that have HSTs with lots of different colour combinations.
• Four at a time - the method I'm showing you here. It's perfect for patterns that have many of the same HSTs, but they have bias edges and therefore distort more easily, which makes them a bit trickier for beginners.
• Eight at a time - essentially a way to quadruple the two-at-a-time method, this technique is perfect for patterns with lots of the same HSTs, and it doesn't have the bias edge issues that the four-at-a-time method has.

I've also created a downloadable cheat sheet for you with diagrams and all the quilty math involved. You can find it at the end of the post to print off and keep the measurements near your cutting table.

A quick note on finished vs. unfinished measurements:

• Finished means the measurement of your unit or block as it is sewn into the quilt. This does not include any seam allowances, and is basically what you see once the quilt top is sewn up.
• Unfinished means the measurements of a block or unit including the seam allowances. So this is what you would see if you measured an HST on your cutting table, before sewing it into a block or quilt. Seam allowances in quilting are normally 1/4", so a quilt block or unit would be 6" x 6" finished, for example, or 6 1/2" x 6 1/2" unfinished. 

Quilt math for four-at-a-time half-square triangles

This method of making four at a time half-square triangles is a slightly trickier version than the two at a time method I showed you in the previous tutorial, because the resulting half-square triangles will have bias edges. This means they will stretch out of shape more easily when sewing, trimming and pressing. A good dose of starch and some careful handling will help with that, though.

There are a few different calculations floating around the internet, and they all end up with weird numbers that aren't exactly standard cutting sizes. So I've done the math for you and compiled the most used sizes this handy chart for you, rounded to 1/4" and 1/2" measurements for easier cutting (you can download a copy of it at the end of the post).

In case you need to make HSTs that finish at a different size than what's in the chart, though, here's how you calculate your starting square size:

Divide the size of the unfinished HST by 0.64, then round up to the nearest 1/4". This method doesn't leave a whole lot of wiggle room for trimming wonky blocks, so you may want to add an extra 1/4" if you prefer to have extra room to trim just in case. The chart above does not include that extra 1/4", so feel free to add it if you need it.

For example, if you wanted to make 4 1/2" finished HSTs, you'd need them to be 5" unfinished. Divide 5" by 0.64, that makes 7.8125" which you would round up to 8". I might leave that one at 8", because the rounding up was already almost a 1/4", but if you're more comfortable with a bit of extra room to trim, cut your starting squares to 8 1/4".

To download a cheat sheet with diagrams and the math chart that you can print out and keep near your sewing table, enter your email address below. You can opt in to my regular email updates as well, if you like, and hear about new tutorials, pattern launches, freebies etc., or get just the cheat sheet emailed to you.

How to make half-square triangles 4-at-a-time

Cut two squares of fabric according to the measurements on the chart.

Place your two squares right sides together.

Sew all the way around the perimeter with a 1/4" seam allowance. You may want to pin your squares together if you notice them shifting.

Place a ruler across the sewn-together squares on the diagonal and cut.

Don't move the fabric, but pick up the ruler and place it down again on the other diagonal, and cut again.

You will have four units cut.

Gently open them up and finger press the seam, making sure not to stretch the fabric, then press by lifting the iron up and down only, don't slide it around on the fabric or push the top triangle over the seam with the iron. Remember, these units have bias edges and are very easily distorted. 

Trim them to the size you need.

How to trim half-square triangles

The easiest way to trim HSTs is by using a square ruler if you have one, but it can also be done with a rectangular one. You can see which rulers I use on my Resources page. There are a few specialty rulers created specifically for trimming half-square triangles as well, but I'm showing you the basic method here.

Line up the 45 degree line on the ruler with the diagonal seam of the half-square triangle. Check that the measurement you need (4 1/2" in our example) is within the fabric on all 4 sides. If not, slide the ruler up or down along the diagonal seam until it fits.

Trim the top and side of the block. I am right-handed, so I am trimming the top and right-hand side of the block, but if you're left-handed, it works the same way on the left, just turn the block around. There are even left-handed rulers that have all the markings the other way around so you're not having to read things upside down.

Turn the block around so the two untrimmed sides are now at the top and right. Line up the 45 degree line again on the diagonal seam, then line up the edges you just cut with the exact measurement you need.

Trim the other two sides.

And there you have it, four HSTs done in one go.

If you don't have a square ruler and are using your rectangular one, here's how that looks. It's lined up exactly like the square ruler, with the diagonal line on the seam and the edges on your chosen markings. I like that my Creative Grids ruler has markings all the way around, but if yours doesn't, just use some masking tape on the ruler to mark the line you need. That should help to keep your eye from slipping to the wrong line.

Quilt patterns that use 4-at-a-time HSTs

Block Adventures is a pattern I co-designed with my friend Katy that uses both 4-at-a-time and 8-at-a-time HSTs to make the various blocks. It was published in Make Modern issue 40 here. There is also a colouring page available if you click on the pattern title above, which takes you to the blog post I wrote about the pattern.