TUTORIAL - Quarter Square Triangles

I remember my first project with half-square triangles. I sewed the squares together, cut them in half, and then trimmed. What did I know about trimming and using the diagonal line as a reference? Nope - I just laid that ruler on and cut out the size I needed. There wasn't a SINGLE point on that quilt. I have since learned how to trim half-square triangles and it is now one of my favorite units.

The quarter square triangle block used to give me grief until recently - yes - even I'm still learning. The day I stop - I'll be dead!!!!    And yes - I still get frustrated and I still make mistakes, but I'm really trying to learn.

So this is what I learned about quarter square triangle block (also known as Hour Glass Blocks) and I'm going to share with you - but you must NEVER confess that you didn't really know how to do them. Once you know these secrets you wonder "why didn't I think of that sooner?"

While this is NOT a tutorial on making quarter square triangle blocks - I have highlighted the critical parts where errors can happen.  (NOTE -  I have ADDED a tutorial further down to walk you through the process step by step. Please scroll down for the detailed instructions on making the quarter square triangle blocks. )

The first part is making TWO half-square triangles (note you can also make QST by using four triangles - I do not use that method)

Make sure the two half square triangles are PERFECTLY pressed. No tucks along that seam at all. Ensure that you are pressing from the right side of the half square triangle - NEVER press from the wrong side of your project.

Ensure the seam of the HST is well pressed in particular the ends

Then place your ruler on the wrong side of one of the HST and lining up a line from the ruler on the seam line - draw a line. 

The KEY - make sure the newly drawn line is 90 DEGREES (perpendicular) to the seam line. Notice the line does NOT necessarily go into the corners of the block. 

Then you sew ¼" on both sides of this drawn line (keep those seam lines STRAIGHT) - the straighter they are - the more perfect the QST block will be. Then cut on the drawn line and PRESS - good pressing just like with the HST ensuring the corners are well pressed.

Then using a ruler (I use the Tucker Trimmer but a regular ruler works, it just has more lines)  - Line up the ruler so that the  FOUR corners of the UNFINISHED size is on each seam line. 

Line up the ruler in preparation for trimming

Trim up the right-hand side and along the top

Rotate the quarter square triangle block (line up the ruler) and trim off the last two sides

A PERFECT quarter square triangle block

Here are the two Tucker Trimmers...................

Tucker Trimmer (this one trims the full inch increments on the one end (note the full black dot) and the other side does ½" increments (note the half-black dot)

Tucker Trimmer II - trims 3/4" increments on one side and ¼" increments on the other

As I said earlier - I am NOT into gimmicks and gadgets anymore - but these rulers are definitely a MUST have if you are into these quarter square triangle blocks (and if you were not before) you will be after you try these.

Remember the same trimming can be done with a regular SQUARE ruler. My preference is 6 ½" square - make sure you have the 1" markings on the top right-hand corner.!!!! If you're left-handed, then the 1" markings should be in the top left-hand corner.


To get started with the quarter square triangle blocks, you need FOUR squares.  In this example, I have one background square, one accent, and two focus fabric squares. You can use TWO background squares instead of one background and one accent. You can also use two squares - one of light and one of the dark.

To determine what size of squares you need, the math calculation indicates that you need to add 1 ½" to the size of the FINISHED unit that I need. So if I need 2" finished units, then I would start with 3 ½" squares. However, that doesn't give you much wiggle room for trimming. So I would add 2". If you're looking for a unit that finishes at 3", then start with squares that measure 5".

Four squares needed to make FOUR quarter square triangle blocks. 

Draw a diagonal line on the wrong side of the background/accent squares

Place the background/accent squares on top of the focus fabric (right sides together)

Stitch a scant quarter inch on either side of the drawn line

Cut the units apart on the diagonal line

Press toward the focus fabric on all FOUR units. DO NOT TRIM

Now take the units with the background fabric and lay them o the units with the accent fabric. Notice that the focus fabric is NOT touching itself!   The focus fabric is next to the background or accent fabric. 

Snug those units tight so that the seam allowances BUTT right up to each other. Because we have pressed the seams to the focus fabric, this is easy. 

Then draw a diagonal line that is 90 DEGREES to the seam line. (see the notes above for clarification). This is very important.   And sew a scant ¼" on both sides of that line. 

Cut the units apart

Twirl the seams on the back (see the tutorial for more on that if you are not familiar with that process)

You now have FOUR quarter square units. 

The last step is to trim the units.   In this example, you can see that they are being trimmed to 2 ½". Look at the diagram in the top part of this post to see the arrows. But note that the 2 ½" lines on the side of the ruler match the seam lines (that will become the corners of the unit). 

And here you have it - nicely trimmed quarter square triangle blocks.

Have a great day!!!!!!!!!!!!!


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