How to Sew a Half Square Triangle - Eight at a Time

Written by Kimberly Coffin · This post may contain affiliate links · 198 Comments

Learn How to Sew Half Square Triangles Eight at a Time With This Sewing Hack, Free Math Measurement Chart, and Step-by-Step Tutorial and Video! This Easy-to-Sew HST Method Is Perfect for Beginners.

Today I'm sharing my time-saving secret for making 8 Half Square Triangles at once! You're going to love this easy-to-sew beginner-friendly method for constructing Half Square Triangles.

Plus, I'm sharing my measurement charts and math cheat sheets to help you get perfectly sized Half Square Triangles for any project. With all of these tips and tricks, you'll be making tons of HST's in no time at all!

A big thanks to JOANN for sponsoring this post. Find all of the supplies in this post at your local JOANN store or on JOANN.com.

Learn How to Sew Half Square Triangles Eight at a Time With My Sewing Secret and Free Math Measurement Chart! This Easy-to-Sew HST Method Is Perfect for Beginners.

Many modern quilt patterns utilize the half-square triangle, and for good reason. It is easy to assemble and can be used to create a multitude of different designs. If you've started quilting recently, learning how to make this block is a must! Let’s dive into this fun tutorial, shall we?

Learn How to Sew Half Square Triangles Eight at a Time With My Sewing Secret and Free Math Measurement Chart!

Table of Contents

Supplies You Will Need and Terms You Should Know

I totally understand, jumping into the craft of quilting can be overwhelming and confusing so before we get into the tutorial for today, let’s go over the supplies you will need to create HST units and some terms I will be using that you will need to know.

Half Square Triangle Supplies

Sewing Machine: You do not need a fancy, expensive sewing machine to create gorgeous quilts.
Thread
Fabric: Quilting cotton is best for this tutorial
Marking Pen: Use a pen with disappearing or water-soluble ink so it won’t show through on your finished quilt.
Cutting Mat
- I prefer a rotating cutting mat for HST
Rotary Cutter: This will help you get precise cuts on your fabric.
Ruler: I would recommend a large ruler around 6”x24” if you are just starting out. This size ruler is really versatile, and you can use it along with the markings on your cutting mat to cut pretty much any size block.
- A square ruler is also great, especially if it's close to the size of your goal size for your blocks.
Iron
Pressing Mat
Pins

Half Square Triangle Quilt Block Tutorial

DOWNLOAD THE FREE MATH CHEAT SHEET HERE!

Terms

Cut Size: refers to what size you cut your pieces before you do any sewing.
Goal Size: also called “unfinished size” this refers to the block after it is constructed but before it is sewn into the quilt.
Finished Size: refers to the block after it has been sewn into the quilt and completed.
Seam Allowance: refers to the excess fabric to the right of the seam. In quilting, the seam allowance is usually ¼” unless specified differently.
Right Side of the Fabric: the “front” or “top” of the fabric where the design is vibrant.
Wrong Side of the Fabric: the “back” of the fabric that is not meant to be seen.

Looking for more free quilting tutorials? Click here!

Half Square Triangles- “8 at a Time” Method

Now that we’ve gathered up our supplies and understand the terms that will be used, let’s get into the tutorial! This method is especially helpful if you need to make several smaller HST units for a project.

Half Square Triangle Cheats and Short Cuts

Step 1: The Math

HST “8 at a Time” equation: Cut size = Goal size + ½” x 2

For this example, I want to create 8 - 3 ½” HST units. So my equation will look like:

Cut size = 3 ½” + ½” x 2

Cut size = 8”

Make sure to add the 1/2" before multiplying by 2!

Since I need 2 squares to create these HST units, I will choose 2 coordinating fabrics and cut 1 - 8” square from each fabric.

Step 2: Cut the Fabric

Pro Tip: When you are cutting with a rotary cutter, it is extremely important to be aware of where your fingers are at all times. You don’t want to accidentally cut yourself with the blade.

Cut 2- 8” squares from the fabric you selected. Make sure you are keeping your ruler stationary on your fabric so you get a perfect, straight cut.

Place your 2 squares right sides together. If you don’t, when you go to sew your squares, half of the HST pieces will be inside out which isn’t what you want.

Line up your squares perfectly. If it will help you, place a few pins in the squares to hold them in place.

Step 3: Mark the Fabric

This is an important step and you want to be sure to make exact marks on the fabric. These lines will be your guidelines when you go to sew the squares together. To draw your lines, line up your ruler diagonally from the top right corner down to the bottom left corner and draw your first line.

Next, do the same thing, but draw the line from the top left corner down to the bottom right corner.

If this is your first time sewing HST's it's helpful to also draw in your cut lines and stitching lines.

Draw a stitching line ¼ inch to either side of each of the diagonal lines.

Next, draw a vertical line from the center of the top to the bottom and a horizontal line from the center of the left side to the right side.

Step 4: Sew the Squares Together

Take your squares to your sewing machine and use your pen markings as guidelines. You will sew ¼” away from each guideline on either side.

After you have sewn both guidelines. It should look like an “x” when you are done sewing.

Step 5: Cut the Half Square Triangle Units

Bring your square back over to the cutting mat and lay it down so it looks like a large “x”. Now we are first going to cut a vertical line from bottom to top in the center of your square.

How to Sew Half Square Triangles Eight at a Time Tutorial

Next, cut a horizontal line from left to right. The cuts should make a large “+” sign.

Take the 4 squares you have now and cut the diagonal guideline on each square to reveal 2 HST units from each square.

Step 6: Press Each Half Square Triangle Block

Using your iron, press each seam from each block towards the darker fabric. Be careful when pressing these blocks that you don’t stretch the fabric.

To press, place an HST unit onto the ironing board with the wrong side of the fabric against the board. Carefully fold open the block and press the seam. Pressing will also help when/if you need to trim the squares down.

Step 7: Trim Excess Fabric

Since we are working with fabric, it is possible that the fabric will stretch even when we are cautious. After you have pressed the blocks, take them back to the cutting mat again and measure them.

Even if you see just a tiny bit of excess fabric, go ahead and trim it off. It may not seem like a lot on one block, but if you left that much on each block, it can greatly mess with the measurements of an entire quilt top.

Tip: To make sure you are squaring up your blocks properly, use the 45° line on your ruler and line it up with the seam of your HST unit. This will ensure you are trimming the square correctly.

Trim all excess pieces and take a moment to admire your 8 beautiful half square triangle blocks!

Wasn’t that so satisfying? Being able to master the construction of the half square triangle is a must for any quilter, and by using this tutorial you will be able to cut that construction time way down!

Quilting is a labor of love and a super exciting and rewarding craft. Don’t forget to have fun with it!