We’ve done the Half Square Triangles and the Flying Geese, so now it’s time to look at Quarter Square Triangles, the remaining commonly used block made using right angled triangles to make a square unit.

There are a couple of different techniques which I use depending on how many units I need and whether I need a particular arrangement of colours.

The traditional method involves cutting the individual triangles, either cutting the triangles individually or by cutting a square into 4 triangles:

Although you are sewing on the bias, this is most useful when you need to control the colour order of the unit, or you only need one unit, such as in a Card Trick block.  They are assembled as follows:

Sew 2 of the triangles right sides together with a 1/4″ seam allowance:

Open out and press:

Repeat with 2 other triangles, then join the two half square triangles you created together:

Open out and press:

If you need a number of units there are 2 method where you can start with half square triangle units.

The first method gives 2 two-tone QST units.

Start with 2 HST units which you arrange as below:

Place right sides together by flipping the left unit on top of the right unit, aligning the 2 units at the corners.  Draw a line on the diagonal going joining the opposite corners to the original seam, then stitch 1/4″on either side of the line.

Cut up the drawn line, open out and press.  You will get two identical units as below:

The second method involves starting with 2 different two-tone HST units.

Start with 2 HST units which you arrange as below:

Place right sides together by flipping the left unit on top of the right unit, aligning the 2 units at the corners.  Draw a line on the diagonal going joining the opposite corners to the original seam, then stitch 1/4″on either side of the line.

Cut up the drawn line, open out and press.  You will get two units as below:

You can see that even if you rotate the second one, it doesn’t come out with the same colour arrangement as the first.  This may or may not be a deal breaker for this method for you:

One of the arrangements that you often see combined are a hybrid of the QST and the HST, such as in pinwheel blocks:

You can create these using either of the methods above, except that in the case of the last two methods you would substitute a square for one of the HST units you start with.

And now to the maths, which is what I know you’re all here for!  In both cases you need to add 1 1/4″ to the finished QST unit size to get your starting square, but I’ve split the columns out just so that you can see at a glance for your chosen method.

Finished QST Unit Size
Traditional Method  Starting Square Size
2 HST Method Starting Square Size
2”
3 ¼”
3 ¼”
2 ½”
3 ¾”
3 ¾”
3”
4 ¼”
4 ¼”
3 ½”
4 ¾”
4 ¾”
4”
5 ¼”
5 ¼”
4 ½”
5 ¾”
5 ¾”
5”
6 ¼”
6 ¼”
5 ½”
6 ¾”
6 ¾”
6”
7 ¼”
7 ¼”
6 ½”
7 ¾”
7 ¾”
7”
8 ¼”
8 ¼”
7 ½”
8 ¾”
8 ¾”
8”
9 ¼”
9 ¼”
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