Magic 8 Half Square Triangles

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Inside: Magic 8 Half Square Triangles

Have you ever needed to make a lot of identical Half Square Triangles (HSTs) for a quilt or other quilting project?

It can be daunting, but not if you use Magic! Here is a way to magically make eight at a time.

Note: Watch the short video that demonstrates how to make HSTs using the Magic 8 Method.


  • (1) 10″ square Blue Fabric
  • (1) 10″ square White Fabric

Basic Sewing Supplies Needed

Step 1:

This method doesn’t require a ton of materials and makes the best use of your fabric. For these Magic 8 Half Square Triangles I used 10″ precut squares which allows you room to square up your blocks when you’re done. If you are confident with your seam allowance, reduce these squares to 9-3/4″ square.

Formula for Calculating any size HST:

There is a math formula to determine the size of the square you’ll need. Double the size of the finished square and add 1-3/4″. (Here’s the math formula for this tutorial: 4″ x  2″ = 8″ + 1-3/4″.) Use this formula to determine any size of Magic 8 HSTs.

How to Make Half Square Triangles using the Magic 8 Method

Step 2:

On the back of the White square, draw 4 lines: one vertically through the center; one horizontally through the center and one on both diagonals. These will be your cutting lines.

How to Make Half Square Triangles using the Magic 8 Method

Step 3:

Place the White fabric on top of the Dark Blue fabric, right sides together. It’s always a good idea to add a couple of pins to keep the fabric from shifting.

 Make Half Square Triangles using the Magic 8 Method

Sew 1/4″ on both sides of the diagonal lines. See this post for help with 1/4″ seam allowances..

Step 4:

Press your sewn block. Don’t move the iron. Just press with a hot iron in an up and down motion. I highly recommend getting a felted wool pressing mat. You will be amazed at how it flattens seams.

Step 5:

Now for the fun part, cutting apart your half square triangles.

You want to lay the uncut block very flat before cutting. If you cut it apart using a rotary cutter, take care not to move the squares with each cut. A rotating cutting mat will come in very handy.

First cut the vertical and then the horizontal lines.

Next, cut the two diagonal lines.

Once you have 8 HSTs, press to set the seams to set them, and then open and press the seams towards the dark fabric.

How to Make Half Square Triangles using the Magic Eight Method

Step 6:

When you have all eight blocks cut, you will need to square them up. Specialty rulers are perfect for squaring up HSTs. Below, I’m demonstrating with one of my favorite rulers.

The Creative Grids Ruler

The Creative Grids 4 1/2″ Ruler is one of the best for squaring up HSTs. It has a diagonal line that matches up with the seam. Notice how it perfectly lines up to square the HSTs. Note: I prefer the 6 1/2″ Creative Grids Ruler because it works for more sizes; however, I do think a 4 1/2″ ruler would be faster because you wouldn’t have to adjust for size.

Creative Grids Rule for trimming quilt blocks

Wasn’t that magical? See how easy it is to make HSTs Eight at a Time. So practice making some HSTs using this method.

How to Make Half Square Triangles using the Magic 8 Method

Now, if you want to make the Midnight Star Table Topper, make two sets of HSTs Eight-at-a-Time using Dark Blue and White fabric. When you are done, you will have sixteen identical HST blocks.

Set these sixteen HSTs aside because they are going to be part of the Midnight Star Table Topper which will be in another post.

Please pin this image!

This block is Part 2 of a fun project called the Midnight Star Table Topper. Below are links to to Part 1 and Part 3, and Part 4.

Part 1: How to Make a Triangle in a Square Block

Part 3: How to Make a Square in a Square Block

Part 4: The Midnight Start Table Topper Pattern 

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