Half square triangles are basic quilt blocks that you may use alone or combined with other quilt blocks to make complex designs. Scroll to the end of this article to see a variety of designs and instructions for each- all using half square triangles! They are used in modern quilting, contemporary quilting, and traditional quilting. Here are 7 ways to make half square triangles.
What is a half-square triangle block?
The half square triangle, also referred to as HST, is a common block in traditional, modern, and contemporary quilting. Use it alone or combine it with other quilt blocks to form more complex patterns for a quilt. This block is a popular ‘stash buster’ to use up scraps of fabrics from other quilting or sewing projects.
Half square triangle is a quilt block with two 90-degree angle triangles, where each of the triangles is half of the square, divided diagonally. It is always a square block.
In this article, we’ll show you the basics of half square triangles and how to sew two triangles together. There are several methods for making half square triangles; some are easier and more accurate. I’ll share my favorites so you can learn from my experiences! Here are seven ways to make half square triangles:
- The basic half square triangle
- Half square triangles two at a time
- Half square triangles four at a time
- Half square triangles eight at a time
- Half square triangles from a charm pack
- Half square triangles from a layer cake
- Half square triangles from a jelly roll
The basics of half square triangles
When you use the basic method starting with two triangles, the long diagonal edges cut on the bias can stretch if over-handled. My favorite method is Half Square Triangles Two at a Time. In this method, you first sew two squares together, then cut them down the middle. The stitches stabilize the bias, so no fiddling with stretchy bias edges.
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Basic half square triangle calculator
Okay, this is when you wish you had paid more attention in geometry class! No worries, we’ve got you covered with this easy formula and cheat sheet for how to cut your fabric for half square triangles.
Start with the size you want your finished quilt block to be. We’ll use the example of a 3″ finished quilt block, which means your sewn half square triangle block will be 3-1/2″ to allow for a 1/4″ seam allowance on all sides.
You’ll want a right triangle, where the corner is 90 degrees. To accommodate the center diagonal seam, we’ll cut the length and height of each triangle at 7/8″ larger than the desired finished size and then cut diagonally from both points.
Here is a cheatsheet on the length and width for the right angle for different size finished half-square triangle quilt blocks:
- 1″ finished blocks, cut the length and width 1-7/8″
- 2″ finished blocks, cut the length and width 2-7/8″
- 3″ finished blocks, cut the length and width 3-7/8″
- 4″ finished blocks, cut the length and width 4-7/8″
- And so on — cut the length and width 7/8″ larger than the finished block size
Step-by-step directions to make a half square triangle
This is the traditional method to make HSTs, also referred to as triangle squares and square triangle units.
Materials needed to make a basic half square triangle unit
- Two coordinating fabrics
- Thread that blends with both fabrics; I use grey a lot
Tools for making half square triangles
- Sewing machine
- Iron
- Ironing board
- Rotary cutter
- Rotary cutting mat
- Quilting ruler
- Optional: specialty rulers for triangles
Instructions making basic HST units
Start by cutting two fabrics the finished size of your block PLUS 7/8″. Here we will make 3″ finished half square triangles, so cut your fabric at 3-7/8″. I went ahead and cut strips because I knew I wanted to make more than one block.
I’ve layered the two strips of fabric on top of each other to cut them at the same time. From the strips, measure 3-7/8″ from the edge and cut diagonally to make a triangle. Here I am using the special ruler by Bonnie Hunter, with markings for the finished block size.
Since I plan on making more than one half square triangle, I can just adjust the ruler to cut another right square triangle at 3-7/8″ on the other horizontal side, using the marking for the 3″ finished block size.
Once you have all of your triangles cut, sew them right sides together on the long diagonal side. This is a bias seam. Be careful not to pull or stretch the fabric on the bias, which can warp your block if stretched.
If you have several to do, the easiest way is to ‘chain piece’ or ‘string piece’ them together. Chain piecing means, as you finish one seam, go ahead and start feeding the next set of fabrics under your sewing machine presser foot. Here you can see my chain of half square triangles I made using the basic method.
Cut the sewn half square triangles apart, press the seams and they are ready to use in your quilt project. Read our article about pressing seams for quilting.
How to make half square triangles two at a time – PREFERRED METHOD
I think it is easier to make two half square triangles at time than to make only one! It’s super easy and you are not matching two bias edges that can stretch when cut.
With this method, you are handling fabric cut on grain and only sewing two seams on the bias and then cutting apart to make two half square triangles.
Half Square Triangles Two (2) at a Time Calculator:
If you want 3″ finished blocks, start with 3-7/8″ squares. Always cut your fabrics 7/8″ larger than the finished block size. The calculation is (finished size of square + 7/8) = cut fabric for 2 half square triangles.
- 1″ finished block, cut 1-7/8″ squares
- 1-1/2″ finished block, cut 2-3/8″ squares
- 2″ finished block, cut 2-7/8″ squares
- 2-1/2″ finished block, cut 3-3/8″ squares
- 3″ finished block, cut 3-7/8″ squares
- And so on . . .
Materials for making half square triangles two at a time
- Fabric large enough to cut out your squares
- Coordinating thread
Tools for making half square triangles two at a time
- Rotary cutter
- Rotary rulers
- Rotary cutting mat
- Sewing machine
- Iron
- Ironing board
- Marking pen; I used a Frixion pen
Tutorial for making half square triangles two at a time
Start by cutting out two squares each 7/8″ larger than the finished final square size. See the calculator above for common sizes.
Mark the center diagonal line on the wrong side of one of the fabrics with a fabric marking pen or pencil. I like to use a Frixion pen. Here I’ve marked both fabrics. You only need to mark one. Select the fabric with the lightest color wrong side. This is your stitching guide line.
Layer your fabric’s right sides together. Make sure one of the fabrics has the marked diagonal line facing up. This is a guide for your stitching. Using a 1/4″ foot on your sewing machine, sew along one side of the marked line.
Turn the piece and sew 1/4″ along the other side of the marked line.
Here is the piece with both sewing lines on either side of the marked line.
Using your rotary cutter, cut down the center forming two half square triangles.
Press open and you have a perfect half square triangle quilt block!
Half square triangles four at a time
This simple method makes four half square triangles at a time.
It is an easy technique, but you need to be careful as all four outside edges of the finished blocks are on the bias and can easily be stretched. I prefer to have the outside edges be straight of grain — but this method is easy if you only need four blocks!
Half square triangles four at a time calculator
When you make these four at a time, it is not exact like it is with making 2 or 8 half square triangles at a time. Always round up from this calculation: Finished half square block size divided by .526. Example: for a finished 3″ half square triangle block, 3/.526=5.7. So, round up to 5.75 or 5-3/4. Then you’ll need to trim your block to 3-1/2″ before sewing together. Here is a cheat sheet for cutting and trimming your fabric for half square triangles four at a time:
- 1″ finished block, 1/.526=1.9; cut your fabric at 2″ and trim cut blocks after sewing to 1-1/2″
- 2″ finished block, 2/.526=3.8; cut your fabric at 4″ and trim cut blocks after sewing to 2-1/2″
- 3″ finished block, 3/.526=5.7; cut your fabric at 5-3/4″ and trim cut blocks after sewing to 3-1/2″
- 4″ finished block, 4/.526=7.6; cut your fabric at 7-3/4″ and trim cut blocks after sewing to 4-1/2″
- 5″ finished block, 5/.526=9.5057034; cut your fabric at 9-5/8″ so that you have a little room to trim and trim cut blocks to 5-1/2″
- 6″ finished block, 6/.526=11.4; cut your fabric at 11-1/2″ and trim cut blocks after sewing to 6-1/2″
- And so on . . .
Materials for making half square triangles four at a time
- Two squares of fabric cut to the chart above or use the formula for other sizes
- Thread
Tools for making half square triangles four at a time
- Sewing machine
- Iron
- Ironing board or pressing mat
- Rotary cutter
- Quilters rulers
- Bloc Loc ruler for block size (Optional, but very helpful)
- Rotary cutting mat
- Rotary cutting mat on turntable
Instructions for making half square triangles four at a time
Cut two squares the right size for your finished quilt block. See the chart above. I’m making 3″ finished quilt blocks so am starting with two squares that are cut to 5-3/4″.
Layer the squares right sides together, matching all four sides, and sew all around all four sides with a 1/4″ seam allowance. Use a 1/4″ foot for your machine. On a Bernina, it is foot #37 or #57. Here I am sewing the first side together.
Continue to sew all four sides together with a 1/4″ seam.
Here is the finished 5-3/4″ square sewn on all four sides.
Take your quilters ruler and rotary cutter and cut diagonally across the square, from corner to corner.
Cut diagonally the other direction to form triangles.
Open them up and press to make half square triangles. NOTE: Be gentle while pressing as all four sides are on the bias and can stretch.
You’ll see that the square is a little larger than the 3-1/2″ square we want for a 3″ finished block size. It’s time to trim the block to the correct finished size. It is measuring about 3-3/4″.
Take your ruler and place the 90-degree line on your diagonal seam. It’s really important to line up that diagonal line on your ruler with the seam line.
Measure to 3-1/2 and trim HSTs on both sides. If you have a smaller square ruler, it makes it easier. Also, if you have a cutting mat on a turntable, it makes it easier.
If you have a BlocLoc half square triangle template for the size of block you are making it is super easy! BlocLoc rulers have a groove that is perfectly placed to line up the seam from corner to corner and keep the ruler firmly in place while cutting.
Here are the four half square triangles all trimmed and ready for my patchwork project!
How to make half square triangles eight at a time
When you need lots of identical half square triangles (HST) and want them fast, make eight at a time!
With this easy and quick method, you can mass produce blocks, and the outside edges are all on stable straight-of-grain – no bias edges! So if you have a quilt pattern with lots of matching half square triangles, this technique is perfect.
Half square triangles eight at a time block calculator
With some easy math, you can make any size HSTs for your next project! Just use this formula. (See common sizes listed below for quick reference.)
To calculate any size HST: Start with your finished block size and add 7/8″, then multiply by two. (Finished block size + 7/8″) x 2 = size to cut fabric squares. Cut two contrasting squares for each set of eight (8) half square triangles.
- 2″ finished block: (2 + 7/8) x 2 = 5-3/4. Cut two squares at 5-3/4″ to make eight (8) 2″ finished half square triangle blocks.
- 3″ finished block: (3 + 7/8) x 2 = 7-3/4. Cut two squares at 7-3/4″ to make eight (8) 3″ finished half square triangle blocks.
- 4″ finished block: (4 + 7/8) x 2 = 9-3/4. Cut two squares at 9-3/4″ to make eight (8) 4″ finished half square triangle blocks.
- 5″ finished block: (5 + 7/8) x 2 = 11-3/4. Cut two squares at 11-3/4″ to make eight (8) 5″ finished half square triangle blocks.
- 6″ finished block: (6 + 7/8) x 2 = 13-3/4. Cut two squares at 13-3/4″ to make eight (8) 6″ finished half square triangle blocks.
- And, so on.
Directions to make half square triangles eight at a time
Cut two squares from your fabric for your finished block, see the chart above. I wanted 3″ finished blocks so I cut 7-3/4″ squares. Draw diagonal lines on the wrong side of one of the blocks with a fabric marker. I used a Frixion Pen. You’ll position the marked side up for sewing.
Place the right sides together, with the wrong side of one of the fabrics on top with the marked diagonal lines. I like to line up my pieces perfectly and secure them with pins so they stay straight while sewing.
Sew 1/4″ to one side of the drawn line with your 1/4″ foot on your machine. On a Bernina it is the 37 or 57 foot.
Turn and sew 1/4″ from the same line on the other side of the marked line.
Turn your layered fabrics 90 degrees. Now sew 1/4″ from the other line.
Turn and sew the final 1/4″ seam.
Now we are ready to cut the layered squares apart to make eight half square triangles. If you have a rotating cutting mat, this is the time to pull it out!
To make the first cut, cut right down the middle of the square, right where the lines and seams intersect in the middle.
Turn, and make the second cut again right down the middle where the lines and seams intersect, making four pieces.
Here are the four sections that were cut.
Next, cut each piece on the marked line to make eight (8) half square triangles.
Finished eight (8) half square triangles ready for a project!
Using precuts to make half square triangles
Precuts are a perfect way to have a variety of fabric in your half square triangles for a quilt. Precuts are fabric collections that are already cut into specific sizes. Charm packs are cut into 5-inch squares, Layer cakes are cut into 10-inch squares, and jelly rolls are cut into 2-1/2 inch strips of fabric that are width-of-fabric, generally 40 – 45 inches long.
If you make an entire quilt with half square triangles using a precut technique, all of your finished squares will be the same size. This makes it super easy to make a coordinated quilt quickly.
If you are going to combine the half-square triangles that you make with a precut, you will need to trim the blocks to match. In each of the sections below, I outline what the finished block size is for each method using a precut.
How to make half square triangles with charm packs
Using charm packs to make your half square triangles makes it easy to have a variety of fabrics without building a big stash. You can make several sizes of half square triangles (HSTs) from a charm pack by using the two-at-a-time, four-at-a-time or eight-at-a-time easy stitch and cut methods.
Charm packs are precut five inch (5″) squares of coordinating fabrics. They can be a collection of solid fabrics that have a theme, or highlight a line of fabrics by a particular designer. Charm packs generally have 42 squares that are 5″ square in each pack.
You can make an easy quilt that looks spectacular by using two coordinating charm packs and turning them into half square triangles two at a time. If you only use charm packs, you don’t need to do a final trim to the squares as they will all be the same size.
Charm pack half square triangles cheatsheet: How many HSTs can be made from a charm pack?
- Two at a time method: you’ll trim to 3-1/2″ and finished square is 3″, making 84 three-inch squares from a charm pack
- Four at a time method: you’ll trim to 2-1/2″ and finished square is 2″, making 168 two-inch squares from a charm pack
- Eight at a time method: you’ll trim to 1-1/2″ and finished square is 1″, making 336 one-inch squares from a charm pack
How to make half square triangles using a charm pack
Use the same directions outlined above for making HSTs two-at-a-time, four-at-a-time, or eight-at-a-time but start with two charm pack fabrics.
Charm pack half square triangles two-at-a-time
Start with two pieces of fabric from a charm pack. Mark the diagonal line.
Sew 1/4-inch on each of the sides of the drawn line.
Use your rotary cutter and cut on the marked line to make your half square triangles.
If you are using only half square triangles from charm packs for your quilt, you can press and begin designing your quilt!
If you are using these in a quilt with other blocks, you’ll want to trim them to a size that is compatible with the other blocks.
Example, if you have a quilt that is using 12″ blocks, you can trim these to 4-1/2 which will be 4″ finished block size, so you can make five sets to make a nine-patch block that has a finished size of 12″. (You’ll have one HST left over to use in another block.) Here I trimmed them to a finished 4-1/2″ size.
Make half square triangles four at a time from charm packs
It’s super easy to make half square triangles (HSTs) four at a time from charm packs. Read above about making HSTs 4 at a time. As I mentioned in earlier in this article, 4 at a time is not my preferred method for making HSTs since the outside edges are on the bias.
Start by layering two charm pack 5″ squares together.
Sew all four sides with 1/4″ seam allowances. Cut diagonally in both directions. Here is the first cut:
Setting up for the second cut:
Here are the four half square triangles after cutting:
Just like the HSTs two at a time above, if you are making a quilt with only these blocks you can go ahead without trimming. If you are using these as part of a larger block, you will need to trim them to the sized needed for your block.
At this stage, they measure about 3-1/4″. I trimmed them to 2-1/2″ so they would work as a 2″ finished block size, which works for 4″, 6″, 8″, 10″ and 12″ block patterns.
Note the waviness of the bias edges and these have been barely touched. This is why this is not my preferred method for making half square triangles.
Half square triangles eight at a time from charm packs
Start by marking one of the 5″ charm pack fabrics with diagonal lines in both directions.
Follow the directions as outlined above for making eight HSTs at a time. Sew 1/4″ on each side of each of the diagonal lines.
Now it is time to cut the half square triangles. Cut along each of the lines, forming 4 pieces.
Then cut through the middle of each, forming eight pieces.
Here are all eight half square triangles cut, ready to press open and then trim.
If you are making a quilt with only these pieces, no need to trim.
If you are using these combined with other blocks, you’ll need to trim them. I trimmed them to 1-/12″ so they will be 1″ finished blocks.
How to make half square triangles from a layer cake
Starting with a layer cake (or two) to make your half square triangles gives you an ever-so-easy variety of fabrics without collecting yards and yards. You can make them using a variety of techniques, so you can make them two-at-a-time, four-at-a-time or eight-at-a-time.
Layer cakes are ten-inch (10″) precut squares of coordinating fabrics, generally from a line of fabrics by a particular designer. There are a total of 42 fabric squares that are 10 inch by 10 inch.
Layer cake half square triangles cheatsheet
You’ll mark, sew and cut two pieces of layer cake fabric together just like outlined above to make half square triangles two-at-a-time, four-at-a-time and eight-at-a-time. To make:
- Two at a time, you’ll trim to 8-1/2″ and finished square is 8″, making 84 eight-inch blocks from one layer cake package
- Four at a time, you’ll trim to 6-1/2″ and the finished square is 6, making 168 six-inch blocks from one layer cake package
- Eight at a time, you’ll trim to 4-1/2″ and finished square is 4″, making 336 four-inch blocks from one layer cake package
Layer cake half square triangles two at a time
Looking for a quick and easy quilt project with a modern look? Purchase two coordinating packs, then turn them into half square triangles two at a time. If you only use one set 10″ squares, then you don’t need to trim the blocks down – they will all be the same size.
Start by drawing a line between two corners on the wrong side of one of your squares.
Layer your two squares right sides together. Sew 1/4″ on each side of the marked line. Use your 1/4″ foot to make it easier. On a Bernina it is the foot #37 or #57.
Once both seams are sewn, use your rotary cutter and cut on the marked line to make your half square triangles from the layer cakes.
Here they are cut apart, ready to be pressed and used in a quilt!
If you are makinq a quilt with only half square triangles from layer cakes there is no need to trim the blocks, as they will all be the same size.
If you are using these half square triangles in a quilt with other blocks you’ll want to trim them to a size that is compatible with the other blocks in your quilt. The 10″ layer cake square trims up nicely to 9-1/2″ square which is a 9″ finished block size.
Here is a finished trimmed half square triangle block from a layer cake.
Half square triangles four at a time from a layer cake
I prefer to make my half square triangles either two at a time or eight at a time, as when you make them using this method four at a time, the edges are on the bias.
Start by layering two squares on top of each other, right sides together. I am using solids, so both sides are the “right” side.
Sew all four sides with a 1/4″ seam allowance.
Then cut diagonally in both directions to make four half square triangles. Here is the first cut:
Then the second cut:
If you are making a quilt with only the half square triangles made four at a time from a layer cake, then you can go ahead and use them without trimming.
If you are using them as part of a larger block, then you will want to trim them to the size you need. These trim nicely to 6-1/2″ for a 6″ finished block which work well for 6″ blocks, 8″ block (when combined with some 2″ blocks) and 12″ blocks.
Here are the finished half square triangles made four at a time. See the waviness on the edges? That is because they are on the bias of the fabric. This is why it is NOT my preferred method of making half square triangles.
Half square triangles eight at a time from a layer cake
Making eight half square triangles eight at a time is a quick and easy way to make a lot of blocks from the same fabrics. When you use layer cakes, you can easily have coordinating fabrics without having to purchase a lot of yardage.
First, mark one of the squares with diagonal lines from corner to corner on the wrong side.
Layer the right sides together. Sew 1/4″ on each side of each of the diagonal lines, right sides together. Here I’m beginning to sew the fourth and final stitching line.
Now it is time to cut the half square triangles. First cut exactly down the middle of the square, through the intersecting seams.
Then, cut the other direction down the middle, forming four (4) pieces.
Then cut each of these along the marked lines, between the stitching lines, to make your half square triangles:
Here are the eight half square triangles from two layer cake squares ready to be pressed and trimmed.
If you are making a quilt with only half square triangles made eight at a time from layer cake squares, no need to trim. If you’ll be using these in combination with other blocks, you’ll want to trim them. These trim nicely to 4-12″ to be used as a 4″ finished quilt block size.
Here is the finished trimmed block at the exact size ready to use!
All eight (8) half square triangle blocks trimmed and ready to use from two squares from a layer cake.
How to make half square triangles from jelly roll strips
It’s easy to make a lot of half square triangles (also referred to as HST) from two jelly roll strips. Jelly roll strips are 2-1/2″ wide strips of fabric that come in a coordinated roll of patterns and colors. Pick two strips from your roll that go well together and make these easy half square triangles.
This is not my preferred method because the edges of the squares are on the bias and may stretch. Be careful when pressing and handling to not stretch your sides. This same method can be used with 2-1/2″ cut strips of fabrics from your stash. This is also referred to as the strip method to make HSTs.
It is best to have a specialty triangle quilters ruler to make half square triangles from jelly roll strips.
Start with two strips of fabric from a jelly roll. Start with a jelly roll. I chose two colors from this bright collection of solid fabrics.
With the right sides together, sew two strips together on both long edges with a quarter inch seam allowance. Here is the first seam.
Next, sew down the other long side with a 1/4-inch seam allowance
Take your triangle quilters ruler and line up the cut size on the seam line. You’ll see I’m lining up the 2-1/2 line on the stitched line.
Cut along both sides to make your half square triangle.
Continue cutting along the sewn strip to make more half square triangles. My strip set made 20 half square triangles.
Scrappy triangles: Tips for making half square triangles
Do you have leftover scraps from a project and don’t know what to do with them? Make scrappy half square triangles for different looks.
Half square triangles make for great leaders and enders when you are quilting. Cut some squares from your stash and when you start piecing, use one for your leader and another for your ender. Then in no time, you’ll have a pile of scrappy half square triangles!
- Cut your scraps from projects into squares that are Finished Size + 7/8-inch.
- Save these in piles.
- Each time you begin to sew, mark the diagonal line on the wrong side of one.
- Layer it right side together with another square the same size.
- Use this as your Leader for stitching.
- Cut it off and sew the other seam as your ender!
- In a short time you’ll have enough half square triangles to make a scrappy quilt!
Layout ideas for half square triangles
There are so many ways to use half square triangles in your quilting. They can be placed together similar to the flying geese pattern:
Put together to form big V’s:
And, even making a herringbone design with your quilt blocks:
No Waste Half Square Triangles
My preferred methods are to make HST two at a time from squares or eight at a time from larger squares. With these methods, you can make HSTs any size and you only need to trim up your final block. There is no waste of trimming off a lot of fabrics or having stretchy bias edges on your HST block.
What are some popular quilt patterns that use half square triangles?
Half square triangles are a very popular component in many quilt blocks and quilt patterns. Here some great half square triangle quilt patterns to make or a great way to use up a stash of HST blocks.
Monkey Wrench Quilt Block uses half square triangles and strip set rectangles.
The cross roads quilt block uses half square triangles and strip sets, too. See how different the same components can look?
The maple leaf quilt block uses half square triangles, solid squares and one split block for the leaf steam.
The swamp angel quilt block uses half square triangles, quarter square triangles and a center square unit.
The card trick quilt block is a traditional block that uses half square triangles, split quarter square triangles and a center quarter square triangle unit.
The double hourglass quilt block version 2 is a traditional quilt block with only half square triangles and squares.
The air castle quilt block is made with half square triangles, square in a square, and split quarter square quilt blocks.
The spool quilt block is made from half square triangles and squares.
The eccentric star quilt block is made from half square triangles and a center square.
The flower basket quilt pattern uses a few different sizes of half square triangles with two rectangular pieces.
Simplex star quilt pattern uses half square triangles and squares to form a star pattern.
Indiana puzzle quilt pattern uses half square triangles and a center block of a square in a square.
The Bear’s Paw Quilt pattern is such a fun one to make with two different sizes of squares and half square triangles.
Friendship star quilt pattern is perfect for baby quilts. It was commonly used for signature quilts.
Shoo fly quilt pattern is a basic nine patch quilt block that uses four half square triangles and five squares.
Calico puzzle quilt pattern is a fun quilt block to make with half square triangles and squares with three different colors of fabrics.
Churn dash quilt pattern uses four half square triangles in the corners, four blocks made with two strips of fabric and a center square.
The basic pinwheel quilt pattern is great for baby quilts or a quilt pattern that looks difficult but is only a collection of half square triangles! Pinwheel blocks put together dance across the quilt top.
Make our cheerful heart quilt pattern with only half square triangles. The heart shape comes together with the fabric choices.
Browse through more free quilt patterns on Create Whimsy. Also, check out our article that covers popular quilt patterns.
