Building Blocks: Half Square Triangles

Hi fellow bakers! This is Mona from Kentucky Whittaker Creations. I’m glad to be back on Moda Bake Shop to share a fun technique with you.

I am not a fan of cutting individual pieces for a project. It never fails – I end up measuring incorrectly or my ruler slips or something else happens. I end up getting frustrated – and then sewing isn’t fun anymore! Because sewing is my sanity-saver and I want to enjoy what I’m doing, I’m always on the look out for new techniques to make cutting easier. This is one of those techniques!

Let’s make some half square triangles!

This technique will allow you to make 8 half square triangles (HSTs) at a time – 4 1/2″ each (4″ finished size)

2 – Layer Cake® Squares (10″ x 10″)

Place 2 Layer Cake® Squares together (right sides together)

Draw a line on both diagonals on the top layer

Sew 1/4″ on both sides of each diagonal (Note – you may choose to pin your layer cake squares together)

Now comes the “magic” – the cutting part. Do your best to not move your layer cake squares. If you have a rotating cutting mat, it will come in handy; however, it’s not required!

Cut along each diagonal (the lines you drew previously)

Next, cut across the width of the layer cake – side to side and top to bottom (assuming that your layer cake is 10″ square, this will be at the 5″ mark)

You should now have 8 individual pieces.

Press to the dark side and trim your HST’s to 4 1/2″.

How easy is that?

Using this technique, you will be able to make 4 1/2″ half square triangles – 8 at a time! So much easier than cutting out all of the individual pieces and sewing them together one at a time!

Thanks for reading along. Please follow me on Instagram to keep up with my latest projects.

Mona Phelps

[blog: Kentucky Whittaker Creations]
[instagram: @mona.phelps]

14 comments on “Building Blocks: Half Square Triangles

  1. Nanette says:

    Do you really take these 41/2”-ish unfinished hst’s and trim them to 2 1/2? It seems like if you want to yield 8 2” finished hst’s you could start with 2 6” squares.

    • Mona Phelps says:

      Hi Nanette – no. I’m sorry – I made a mistake when typing up the post. You will actually get 4 1/2″ HST’s. My apologies!! I’ve updated the post and Oda May will update the printable.

  2. Maggie A Drafts says:

    Well, Mona, that is an excellent idea; however is there a “chart” for making HST bigger than 2.5 inches? How big would you cut the squares for bigger HST???? (I do not figuring out the math!!!)

    • Mona Phelps says:

      Hi Maggie – I’m sorry, I don’t have a chart. I figured this out when playing around with layer cake squares. Someone else may have something. Or maybe searching the internet? Thanks!

  3. Alora says:

    My comment is more of a question. How do you determine the size of the original squares to make a certain size HST? I just made a wall hanging that used charm squares and I got 8 2″ HSTs out of 5″ squares. You used a 10″ square to get 8 2-1/2″ HSTs. There must be a formula.

    • Mona Phelps says:

      Hi Alora,

      I made a mistake and put the wrong measurement in the post. These will result in HST’s that are 4 1/2″. I’ve update the post – I’m sorry!


  4. Pat D says:

    She trims them DOWN to 2 1/2 inches. She is chopping a lot of the fabric off!

    The formula is add 7/8″ to the finished size of the HST to get the size of the square you need to cut. Reversing the formula, and using the ‘Easy Eight’ layer cake method, you are cutting 5 inch squares (cut once diagonally). Subtract 7/8″ from the 5 inch, leaves you with a 4 1/8″ finished HST. To allow for seam allowance differences, most people trim them to 4 1/2 which gives you a 4″ finished HST.

    I’m thinking she could have started with a 7 inch square, to get to the 2 1/2 finished HST.

    Also the ‘finished’ size does not include seam allowances. So her final step that said to trim them to 2 1/2″ is misleading. You actually trim the HST to 3″ to get a 2 1/2″ finished block..

  5. Rachel says:

    Wow, fabulous idea! Thank you for sharing that tip…this would work great for making pillows or a simple table runner. I admit there are some boundaries for the finished sizing, but your tip was for using layer cakes or for a 2-1/2 HST…so I get it. 😉 If using yardage you could revert back to the traditional methods or figure out the new sizing on your own. This is just one of SO many options for HST! Brilliant in my opinion! 😀 Thank you!

  6. Sharon L Schmidt says:

    I like to make the left/right and top/bottom cuts first. That way if my fabric jiggles when cutting, I still have the seams as a guide for the diagonal cuts. Thanks

  7. Sherly says:

    Thank you so much for this awesome mini lesson as a newbie I can’t wait to try it.

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