Welcome to my updated and expanded tutorial on how to make perfect quarter square triangle units. Since I first published it in 2012, this has been my most popular tutorial ever – thank you Pinterest! Now it’s 2018 and I thought it was time to give it a fresh look with better images and more detailed instructions. Plus, I’ve included a cutting chart that you can download and print out. Towards the end, you’ll find instructions on how to make the popular Ohio Star block which includes four quarter square triangle units. Enjoy!
Original quarter square triangle photo used for the Ohio Star:
Quarter Square Triangle Math
You start with four squares to make four quarter-square triangle (QST) units. First, let’s talk numbers (I know, it’s an evil necessity). In order to know the size of the squares to start with, you need to know the finished size of the unit, which is 3″ in this case (that’s because I want a 9″ finished size block). Add 1 1/4″ to that number and you have the size needed to cut your squares. So, 3″ + 1 1/4″ will give us 4 1/4″ squares.
Now, if I were a perfect quilter, I would use that number. However, things often get a little wonky on me, so I like to oversize my QST’s so that I can trim them down into the perfect size. So, I add 1 1/2″ to the finished size desired. For this unit, I will need (4) 4 1/2″ squares to start with.
Download my over-sized cutting chart for 11 different sized quarter square triangle units here: Quarter Square Triangle Cutting Chart
Quarter Square Triangle Construction
First, draw a diagonal line on the two like-colored squares from corner to corner. Use a pencil or Frixion Pen (my favorite) and a ruler to draw your line. You’ll be stitching 1/4″ on each side of the line. If you don’t have a 1/4″ foot, you might want to draw the actual stitching lines. A special ruler called the Quilter’s Rule Quick Quarter II makes this step easy. Some people find it easier (and more precise) to stitch on a drawn line instead of 1/4″ away from a line. The following picture shows both ways:
With right sides together, layer each red square with another square and stitch 1/4″ on either side of the center drawn line (or exactly on the drawn lines if you chose that method). Cut apart between stitching lines and press towards the red square. You should now have four half-square triangles (HST’s).
Next, layer two of the HST’s together so that the center seams nest together and the red colors are opposite each other.
Again, you’re going to draw a diagonal line and stitch as you did in the previous step.
UPDATED TIP: It’s important to draw the line so that it’s perpendicular to the seam. Instead of only lining up the ruler with the corners, make sure to also place a line of your ruler on the seam when you mark your line. If the corners don’t line up exactly, that’s o.k.
I think it’s important to pin the seams that are nesting and to stitch with the top seam allowance facing up (towards the machine needle):
TIP: Why does it matter if the top seam allowance is facing the needle? Because if I were to start stitching at the top and the seam allowance was facing away from my needle, chances are the presser foot would push the top seam allowance down and away from the bottom seam. But because I have my seam allowance on top facing the needle, the presser foot still pushes the top seam allowance, but it pushes into the bottom seam allowance creating a more snug intersection. That’s a lot of information, but if you’re new to quilting it’s nice to know these little tricks.
Now you’re going to cut these apart between your stitching lines and, voila, you have your QST’s!
Now remember we still need to trim these units down to 3 1/2″ square. There are several ways of doing that. For the first two methods, you will need to press your seam before trimming. You can press to one side or twirl your seam allowances. I like to “twirl” my seam allowance because it makes the unit flatter and my ruler doesn’t rock when I’m cutting.
To do this, you’ll press half of the seam allowance up and the other half down. The center (where the 4 seams intersect) should pop open in the seam allowance, creating a mini 4-patch in the center of the wrong side.
Trim method 1
You will need a square ruler that is 3 1/2″ or larger. Place it so that the diagonal line of the ruler is along one of the diagonal seams of your QST. You need to make sure that you’re trimming the same amount equally from all four sides so that your center seam stays in the center. So, put the 1 3/4″ intersection of the ruler (that’s half of 3 1/2″) at the center seam and trim along the top and right hand side (if you’re right handed).
Now rotate the QST and line up the 3 1/2″ lines of the ruler with the previously cut edges. Trim the remaining two sides. You should now have a perfect 3 1/2″ QST.
Updated: Trim method 2
For the second method of trimming, I love the Tucker Trimmer 1 by Studio 180 Design. This ruler does a fantastic job of trimming down pieced squares accurately and easily. It can be used on HST’s and QST’s. There are two diagonal markings to line up with the seams on the QST which takes the guess work out of the ruler placement.
Trim method 3
This method uses a ruler that I’ve had for a long time – Quilt In A Day’s Triangle Square-up Ruler. The advantage of this ruler is you trim two sides at the same time, and it has two diagonal markings for easy placement.
Before pressing your seam, you will place the ruler so that the 3 1/2″ red dashed line is along the bottom stitching line and the perpendicular line is placed along the center seam. Now you just have to trim the two sides and then press!
Ohio Star Quilt Block
If you want to make a 9″ (finished size) Ohio Star Block, you will need (4) 3 1/2″ squares and (1) 4 1/2″ square of background fabric, (1) 3 1/2″ center square, (2) 4 1/2″ squares of medium fabric, and (1) 4 1/2″ square of dark fabric. (You can also interchange the medium and dark fabrics.) I’m using fabric from the Farmhouse collection by Fig Tree for Moda.
First, make the 4 quarter-square triangle units using the instructions above. Then arrange your squares as shown below and sew them into rows. Press seams toward the plain squares.
Now join the rows together. When pinning the rows together, make sure to use a setting pin at the intersections so that your diagonal seams will match and there will be a visual straight line as shown below.
Here’s how a setting pin works: Nest your seams together. Starting on the top seam allowance, there should be an “x” where the stitching lines are. Place your setting pin straight down through the “x” and then straight down into the bottom seam allowance’s “x”. Leave that pin straight up and down (perpendicular) to the seam. You can peak to see if the diagonal seams match up by pinching the intersection with your fingers and opening it up. Then pin on either side of your setting pin, close to the seam allowance. Remove the setting pin and sew your seam, making sure your stitching goes through the middle of the “x”.
2018 update: Using washable glue instead of pins has become very popular for matching seams. I recently purchased Seam Align Glue by Acorn Precision Piecing from The Quilt Show and I used it for this quilt block. I love it! It was easy to apply and it didn’t make the fabric stiff. My seams came out perfectly. Elmer’s Washable School glue would work also.
Your block should measure 9 1/2″ square.
I love making quarter square triangles and they’re so versatile! Maybe I’ll make enough Ohio Stars for a table runner (in my spare time!) or I might just quilt it as is and practice my free motion quilting (more likely). Thanks so much for stopping by!