Quarter-Square Triangle Tutorial

I’m back with a tutorial on how to make quarter-square triangle units. I used them in Block 1 of the “Paris In The Fall” BOM post from a few days ago. In today’s tutorial, I have made them into an Ohio Star block.

You will need 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. This will give us 4 1/4″ squares.  Now, if I were a perfect piecer, I would go with 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.  They should look something like this:

You will need to draw a diagonal line on two of the squares (I chose the red ones) from corner to corner. Use a pencil or other marking tool and a ruler to draw your line. I like to draw the actual stitching lines using a special ruler called the Quilter’s Rule Quick Quarter II . You could also use a regular ruler to draw those lines as well. Again, I need all of the help I can get and it’s easier for me 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 either 1/4″ on either side of drawn line or exactly on the drawn lines (if you do it like me). Cut apart between stitching lines and press towards the red square. You should now have four half-square triangles (HST’s) that look like this:

Now you will layer two of these HST’s together so that the center seams nest together and colors are opposite each other:

Again, we’re going to draw diagonal lines and stitch as we did in the previous step. I think it’s important to pin the seams that are nesting and to stitch with the top seam allowance facing the needle like so:

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. Wow, that was 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 on the diagonal between your stitching lines and, voila, you have your QST’s!

Now remember we still need to trim these puppies down to 3 1/2″ square. There are two ways of doing that.  For the first method, you will need to press your seam to one side before trimming.  You will need a square ruler that is 3 1/2″ or larger and you are going to place it so that the diagonal line of the ruler is along one of the diagonal seams of your QST. You also 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 at the center seam as shown below:

Trim along the top and right side.  Now rotate the QST and trim remaining two sides.  You should now have a perfect 3 1/2″ QST!

For the second method of trimming these down, I like to use Quilt In A Day’s Triangle Square-up Ruler. It looks like this:

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 like this:

Now you just have to trim the two sides and then press!

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″ square and (2) 4 1/2″ squares of dark fabric, (1) 4 1/2″ square of medium fabric.

First, make the 4 quarter-square triangle units using the instructions above. Then you will arrange your squares like so:

Sew them together into rows and press seams toward plain squares:

Now all you need to do is join your rows together.  When pinning the rows together, make sure to use a setting pin at the intersections so that your diagonal seams will have a straight line to them as shown in this picture:

Here’s what a setting pin does:  Nest your seams together and starting on the top seam allowance, there should be an “x” where the stitching lines are. Place your 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.  Then pin on either side of your setting pin, close to the seam allowance.  Remove setting pin and sew your seam, making sure your stitching goes through the middle of the “x”. Your pin placement should look like this:

It’s hard to see, but there is a setting pin going straight down through the middle of the intersection. Here’s another look at the finished block:

And here’s Block One of the Paris in the Fall Block of the Month:

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). Leave me a comment if you have any other ideas!



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About Julie Cefalu

Hello! I'm Julie and I love to quilt, craft, read, garden, hike and spend time with my family.

22 thoughts on “Quarter-Square Triangle Tutorial

  1. This deal is a huge net loser for the NJ taxpayer. Who do you will cover the losses for Monmouth (and they will be huge). The stark reality is that running for low purses will greatly effect field size, which in turn will effect handle. Allan

  2. Thank you. I needed to know how much bigger the quarter square triangle’s square needed to be to fit my finished square’s size.

  3. I have a chickadee panel that measures 7 inch square and would like to make it into the Ohio star block – how big should I cut the squares to make the triangle squares and what do I cut them down to.
    I have been looking at your site and really like it – I am fairly new to quilting so aren’t always sure of measurements. Thanks very much Lesley

  4. need formula to make a (what is called) 3 patch quarter square triangle. want a finished 4″ (unfinished 4 1/2″)
    thanks so much.

  5. I would like to ask you a question? I’m making a lot of flying geese blocks and need to know the measurements for a flying geese that will be 2×3-1/2 in the quick method way. If I’m not asking in the right terms. Please contact me and I can explain better. Thank you
    Mary McCormick
    My phone number is 707-331-5318
    I live in Santa Rosa, California

    Thank you very much

  6. Very well done and EXTREMELY helpful! A good teacher is one that is understood and you are very much that! Thanks.

  7. Thanks for the tutorial. Wish I had read it BEFORE I started on this block. But now I know that I need to add 1 1/2″ to size of original blocks. Thanks. I have pinned it so I won’t have to find it again.

  8. Your tutorial is fantastic! I’m not new to this technique, but you explain it better than I’ve ever seen it explained – even a beginner should have no problem. I think its so important to know the 1 1/4″ (or 1 1/2″) rule, which sometimes gets left by the wayside. That triangle square-up ruler is totally cool – definitely now on my wish list. Thanks so much! Now I’m off to see what other great tutorials you have. Oh and thanks for your nice comment on my blog.

    1. Bless you. Best of all I’ve searched for visual and logical, complete info. Been quilting (stashing) since mid 80s, now that I’ve retired, so many changes in techniques. I initially learned with drafting paper patterns, and scissors. Currently renewing my piecing skills. Thank you again.

  9. I am brand new to quilting and confused with precise measurements for different sized quarter triangles please and half triangles.
    Thank you,

    1. Sorry my message was sent in error.
      I am trying to work out quarter and half triangles to get their precise measurement before putting together. Can you help with the different sizes please. I am brand new to patchworking and rather confused with the measurements for these pieces.
      Thank you and sorry for previous message sent in error.

  10. Thank you Julie!! Your written instructions & photos are very clear in showing “how to.” Your seam points are so precise — gives me something to shoot for.

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