How To Use A Quarter Square Triangle Ruler Tutorial

How to use a quarter square triangle ruler... With this essential quilting tool you can easily make split, 3-patch or hourglass quarter square triangles (a.k.a. QSTs) used in quilt blocks.

Picture of a Creative Grids (R) quarter square triangle rulerCreative Grids (R) quarter square triangle ruler

Quarter Square Triangle Rulers

Some QST rulers have a blunt tip (like the one in the photo above) to replace offsetting triangles when stitching.

Picture of a closeup of a Creative Grids (R) quarter square triangle rulercloseup of a quarter square triangle ruler with 1/4 inch measurement lines

Other rulers have a pointed tip (photo below) which may have a blackened triangle tip or it may not.

Picture of a Fons and Porter (R) quarter square triangle rulerFons and Porter (R) quarter square triangle ruler

If you use a ruler with a pointed tip that has no blackened triangle tip you may need to manually offset the triangles by 1/4 inch before stitching. Check the instructions for your ruler.

Examples of Quarter Square Triangles

Here are examples of quarter square triangles as mirror image split quarter square triangles with fabric placement in different spots. You will see later in this tutorial how important stitching becomes.

split quarter square triangles

Quarter square triangles as hourglass blocks. The QSTs are non-mirror images, or the same...

Quarter square triangles as hourglass blocks

Quarter Square Triangle Ruler Math

A single quarter square triangle (QST) is twice as long as it is tall. Four QSTs make a square.

Divide the finished unit size by 2 and add 1/2 inch for the seam allowance.

(Finished Unit Size / 2) + 1/2 inch

As an example, a 2 inch finished size unit is

  • 2 / 2 = 1 + 1/2 = 1 1/2 inches

How do you make quarter square triangles out of strips?

To make QSTs using a quarter square triangle ruler, cut 2 strips and align with right sides together. Place the ruler's measurement line along the bottom edge of the strips and cut.

To make a quarter square triangle using a QST Ruler for the above example size:

cut 2 (1 1/2 inch) strips, align with right sides together, place the 1 1/2 inch ruler measurement line along the bottom edge of the strips and cut.

How To Use A Quarter Square Triangle Ruler Instructions

Step 1 Place the correct measurement line of the quarter square triangle (QST) ruler along the bottom edge of the strip. (I am demonstrating our above example so I align along the 1 1/2 inch ruler measurement line.)

Place the left side of the ruler to the right of the selvage edge (or uneven edge).

Use a rotary cutter to cut the strip along the right and left sides of the ruler.

Step 1 How To Use A Quarter Square Triangle Ruler: Place measurement line of  ruler on bottom edge of strip, place left side of ruler to right of selvage edge, cut strip along right and left of ruler.

Note: If your QST ruler has a pointed tip that is blackened or highlighted align the bottom of the blackened or highlighted triangle along the top edge of your fabric strips and the ruler's measurement line along the bottom of the fabric strips.

How To Use A Quarter Square Triangle Ruler: align bottom of blackened or highlighted triangle along top edge of strips and ruler's measurement line along bottom.

Step 2 Rotate the ruler 180 degrees so that the blunt (or pointed) tip is aligned along the bottom edge of the strip set.

Align the left side of the ruler along the left side of the previous cut. Make a cut along the right side of the ruler, making a second QST.

Step 2 How To Use A Quarter Square Triangle Ruler: Rotate ruler 180 degrees, align tip on bottom of strip, align left edge of ruler with previous cut. Cut along right side of ruler.

Step 3 Continue to rotate the ruler 180 degrees, aligning the ruler as in Steps 1 and 2 and cut QSTs until you have cut all of the QSTs you need or allowed by the length of the strips.

Step 3 How To Use A Quarter Square Triangle Ruler: Continue to rotate the ruler, aligning the ruler as in Steps 1 and 2 to cut QSTs.

Stitching Quarter Square Triangles Cut from Strips

Stitching the QSTs matters. The fabric on top when the QST goes under the needle will be on top when the fabric is flipped right side up.

In the photo below, I stitched the first QST with the white fabric on top and the 2nd QST with the black fabric on top.

How To Use A Quarter Square Triangle Ruler: The fabric on top when the QST goes under the needle will be on top when the fabric is flipped right side up.

This will result in mirror image QSTs. As you can see in each set of these quarter square triangle the position of each color of fabric is different. They are mirror images of one another. Be mindful of this when making your own blocks or stitching your own quilt patterns. Commercial quilt patterns will tell you how to stitch the quarter square triangles.

How To Use A Quarter Square Triangle Ruler: As you can see in each set of these quarter square triangle the position of each color fabric is different.

You can see why this is important when the QSTs are fully stitched into a unit used in a quilt block. For example, the Scottie dog quilt block.

How To Use A Quarter Square Triangle Ruler: You can see why this is important when the QSTs are fully stitched into a unit used in a quilt block.

If you stitch all of the quarter square triangles with the same fabric on top...

How To Use A Quarter Square Triangle Ruler: If you stitch all of the QSTs with the same fabric on top...

...all of the quarter square triangles will be identical, or non-mirror image, units with fabric placement the same.

How To Use A Quarter Square Triangle Ruler: ...all of the quarter square triangles will be identical units with fabric placement the same.

How to Use a Quarter Square Triangle Ruler: Cutting Tip

When cutting the first QST from the strip if you do not want to cut towards yourself, cut the first QST in two steps.

Make the first cut along the right edge of the ruler.

How To Use A Quarter Square Triangle Ruler: cut the first QST in two steps.
Make the first cut along the right edge of the ruler.

Rotate the fabric and the ruler 180 degrees and make the second cut.

How To Use A Quarter Square Triangle Ruler: Rotate the fabric and the ruler 180 degrees and make the second cut.

This tutorial gives directions on how to use a quarter square triangle ruler, but there are many ways to make and arrange quarter square triangles...

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