Half Square Triangle: A Quilter’s Best Friend
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The humble Half Square Triangle (HST) is proof that sometimes the simplest shapes create the most stunning quilts. Whether you’re a beginner piecing your first block or an experienced quilter planning a show quilt, HSTs will always have a place in your toolbox.
The half-Square Triangle
If you’ve been quilting for any length of time, you’ve probably worked with Half Square Triangles (HSTs). This simple yet powerful quilt block unit is one of the most versatile building blocks in quilting. From traditional classics to bold modern designs — HSTs can do it all.
Mastering this basic quilt block opens the door to so many design possibilities. The Half-Square Triangle (HST) shows up in hundreds of quilt blocks and can also be used to create other favorite units like the Quarter-Square Triangle and Flying Geese.
What is a Half Square Triangle?
A Half Square Triangle is exactly what it sounds like: a square that’s divided diagonally into two equal right triangles. With two contrasting fabrics, you get a clean, graphic unit that adds movement and interest to any quilt.
Quilters have been sewing Half Square Triangles for centuries. You’ll find them in some of the earliest American patchwork quilts, often used to create star blocks, pinwheels, or geometric borders. Their timeless appeal is part of why so many quilt patterns still rely on them today.
From Humble to stunning
With just a few Half-Square Triangles, the design options are endless! Rotate them, mix fabrics, or pair them with plain squares, and you can create pinwheels, diamonds, hourglasses, chevrons, and so much more. Just check out the images below.
HSTs may be simple, but their potential is huge—just a few units can inspire countless quilt designs. Let your creativity run wild!
The quilt blocks below are made using only HST units.
Add a few plain squares, and suddenly you have blocks like the ones below, featuring a mix of HST units and simple squares.
Tips for Success
- Oversize and Trim – Make your HSTs slightly larger than needed and trim down to ensure precision. The directions below show you how to do that.
- Pressing Matters – Consistent pressing (open or to one side) helps seams nest perfectly.
- Make Multiples – Want to save time? Make multiple HST’s at once instead of one by one.
- Chain Piecing – Save time by sewing multiple HSTs in one go.
- Use a Trim Tool – Every quilter has a favorite – find the trim tool for HSTs that feels just right for you.
- Stop Drawing Diagonal Lines and start using Diagonal Seam Tape from Cluck, Cluck Sew! The instructions below show a conventional method for making HST units, but you might find the Cluck, Cluck Sew method even easier.
Make Multiple HST units at Once
Depending on the amount of fabric you have and the number of HST units you need, there are several methods you can use to make multiple HST units at once.
There’s no single “right way” to make HSTs—just the method that works best for you. Here are a few popular options:
Quick Half Square Triangle Trick for Small Squares
This trick works wonders with small pieces. Two 3″ × 3″ fabric squares will make two 2½” HST units—perfect for trimming and adding to your quilt.
- Place two 3″ x 3″ fabric squares right sides together.
- Draw a diagonal line on the wrong side of one square.
- Sew ¼” away from the line on both sides.
- Cut along the diagonal. Press open—your HSTs are ready!
Create 4 Half Square Triangle Units at a Time
If your fabric squares are at least 4½” square, you can make four 2½” × 2½”HST units at once.
- Place two 4½” x 4½” fabric squares right sides together.
- Sew all around the edges (dashed line).
- Cut along both diagonals (red lines).
- Trim each HST to 2½” × 2½”—perfectly ready to add to your quilt!
You can make a surprising number of quilt blocks with just four HST units! This method is a great way to put a charm pack to use—a single charm pack has 42 five-inch squares.
Using this technique, you could end up with 168 HST units measuring 2½” × 2½” – enough for lots of fun quilt blocks!
Friendly Tip: Try mixing and matching fabrics for your four HSTs—you can create mini scrappy blocks that add a fun pop of color to your quilt!
Make 8 Half Square Triangles at a Time
If you’re working with yardage or fat quarters and need as many as eight 2½” × 2½” HST units, this technique is perfect to try.
- Place two 6¼-inch fabric squares right sides together
- On the wrong side of one of the fabric squares, draw diagonal lines from corner to corner to form an “X.”
- Sew around the edges of the square (dashed line).
- Sew ¼” away from each diagonal line on both sides (diagonal dashed lines).
- Cut the sewn unit in half horizontally and vertically (red lines).
- Cut along the drawn diagonal lines.
- Press each HST open and trim to 2½” × 2½”.
How about 16 Half Square Triangles at one time?
The last technique can be done with yardage, fat quarters, or – most conveniently – a layer cake. Using this method, you can make 16 HSTs at once that can be trimmed to 2½” × 2½”.
- Place two 10-inch fabric squares right sides together.
- On the wrong side of one square, draw a horizontal line and a vertical line at the midpoint (solid black lines below).
- Sew ¼” away from each drawn line on both sides (see dashed lines).
- Sew around the edges of the 10″ square (dashed lines).
- Cut the sewn unit in half along the drawn horizontal & vertical lines (solid black lines).
- Cut each of the resulting [4] square units on the diagonal twice (solid red lines).
- Press each HST open and trim to 2½” × 2½”.
Find your Perfect HST Trim Tool
As mentioned earlier, the key to perfect Half Square Triangle units is sewing them slightly larger and then trimming them to the exact size. Fortunately, there are plenty of tools available to make this process easier.
Find a trim tool that works best for you. I like using the Creative Grids 6½” Square Quilt Ruler because it’s handy for much more than just trimming HST units (squaring blocks, cutting small strips, etc.) That said, there are several specialized rulers on the market that might suit your needs even better.
Bloc Loc HST Ruler: Renowned for its groove technology that locks onto the seam, ensuring precise trimming without slipping. Ideal for quilters who prefer pressing seams to one side. Bloc Loc Rulers
Creative Grids Half Square 4-in-1 Triangle Ruler: Offers versatility with multiple size options and a non-slip grip, making it a great all-around choice for various HST sizes. Creative Grids
Quilt in a Day Triangle Square Up Ruler: A budget-friendly option that provides clear markings and is suitable for beginners looking to square up HSTs and Quarter Square Triangles (QSTs). Quilt in a Day Triangle Square Up Ruler
Why Quilters Love Half Square Triangles
- Endless Design Possibilities – Arrange them in rows, diamonds, chevrons, or stars. A quilt made entirely of HSTs can look modern, traditional, or anywhere in between.
- Great for Beginners – Once you learn the basics, HSTs are approachable and forgiving if you use the trim approaches described here.
- Scrap-Friendly – They’re perfect for using up those fabric leftovers in your stash.
- Scalable – Whether you need a 2” block or a 10” block, HSTs adapt easily to any project.
The possibilities are endless, and that’s why HSTs remain one of quilting’s most beloved elements.
