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Half Square Triangle Tutorial

Half square triangles are, in my opinion, one of the most versatile blocks you can make. You can do all sorts of things with them and they’re great for using up your scraps.

Here’s how to make one.

Cut out two squares that are the same size. These 2 blocks are 5″ squares.


Place them right sides together.


Using your quilt ruler, draw a line down the center, from corner to corner. It doesn’t really matter what you use to draw your line as long as you can see it because your going to be cutting down it with your rotary cutter. I used a regular ball point pen.


Now you’re going to sew down both sides of the line using a 1/4″ seam allowance. Look at the pictures below if you need help. And this another time where a 1/4″ foot comes in so handy. I don’t know how I lived without mine for so long.


After you sew all the way down, you’re going to cut the thread and sew on the other side of the line.


Now take your block and use your rotary cutter to cut along the line you drew earlier.


You’ll have these…


Now iron each one open. I iron my seam towards the darker fabric.


Then I like to flip it over and iron the “right” side, too. I think it makes it a little smoother and easier to work with, but it’s really not an absolutely necessary step.


Now square your blocks up. When you square them up, make sure you’re squaring them all up to be exactly the same size. For example, if you started with two 5″ fabric squares, like I did, at this point should have a 4.5″ half square triangle block. Go ahead when you’re squaring them up and make sure all your blocks for your quilt are 4.5″ square, and you’ll save yourself a lot of frustration when you’re piecing your blocks together later on.

Just a quick story… I’m making these for the quilt I’m working on right now. I’m not sure what I did wrong, but I when I was squaring up these blocks, I saw that several of them were slightly less than 4.5″ square. So to save myself some heartache and frustration when I was piecing my quilt blocks, I went ahead and made them 4.25″ square. It’s not going to hurt a thing, it’ll just give me a slightly smaller quilt.


You’ll have these when you’re done.


I love these little half square triangles because you can make so many different things with them.

Their most popular use is probably in a pinwheel block.


But you could also make a diamond.


Then reverse it for a totally different look.


You can make rows. I know this doesn’t look like much, but imagine an entire quilt. I think it’d look really neat.


These are just four really simple examples. You can play with them and come up with lots more. If you want to try designing a quilt using them, get some graph paper and sketch it out first.


  1. Oh my! I’ve been making quilts for only a year and never thought of cutting my half square triangles that way! How much easier to draw your line, sew both sides THEN cut! I’ve been cutting my triangles and then sewing them together. THANKS!

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