Essential guide to making half-square trianglesSee more from Today's Quilter magazine
Find out everything you need to know about making half square triangles for all your patchwork and quilting needs!
METHOD 1: TRIANGLES SEWN TOGETHER – MAKES 1 UNIT
The simplest way to make an HST is to sew two triangles together. It’s easy but not the most efficient or fastest way if you need to make multiple units (as we often do!).
The triangles need to be cut 7⁄8 in larger than the desired finished size. This may seem like an odd fraction but Fig 1 shows why.
Cut a right-angled triangle from two different fabrics, cutting each triangle the finished size you want plus 7⁄8in. (Alternatively, cut a square and sub-cut it into triangles.) You can pre-trim the points at this stage if desired (see below).
Place the triangles right sides together, aligning the long edges, and then pin. Sew the seam ¼in from the edge
Open out the unit and press the seam (open or to one side as preferred). Check the size of the unit and make sure it is the size needed and also square.
Before sewing triangles together you can use a Point Trimmer gadget to trim off the points, to save removing the dog ears later. This produces fat corners on the triangle, which makes the seam easier to sew. However, on smaller triangles such gadgets may trim of too much and lead to inaccuracies, so use with caution.
METHOD 2: SQUARES SEWN TOGETHER – MAKES 2 UNITS AT ONCE
One of the most popular ways to make HSTs is with two squares, which makes two identical units. These can be chain-pieced for speed if you need many units.
The squares need to be cut the size that you want your sewn unit to be (i.e., the unfinished size), plus 7⁄8in. So, for a 2½in unfinished HST cut the starting squares at 3 3⁄8in or round up to 3½in. The sewn unit can then be trimmed down to an exact 2½in
Cut one square from two different fabrics. Pencil mark the diagonal line on the wrong side of the lightest square. Place or press the two squares right- sides together, with all outer edges aligned (Fig A below).
Pin the squares together and sew ¼in away from the marked line on each side (Fig B above).
Press the stitching and then cut the units apart on the marked line.
Open out each unit and press the seam (open or to one side as preferred). Check the size of each unit and make sure it is the size needed and is also square (right angled).
METHOD 3: SQUARES SEWN TOGETHER – MAKES 4 UNITS AT ONCE
If you have quite a few HST units to make, then making four at once is quicker. All units are identical and start off as squares. The squares are cut slightly over size and then the sewn units are trimmed down to the exact size needed.
Calculate what size of squares you need to cut (see the Maths Made Easy box at the bottom of this section). Cut a square from two different fabrics. Place them right-sides together, matching all edges exactly and pin.
Sew around all four sides of the square ¼in away from the edge
Carefully cut the sewn squares into quarters along the diagonals (marked in red lines on the diagram above), so you end up with four triangles.
Take each unit, open it up and press the seam open or to one side. Check the size of each HST, trimming as needed.
Maths made easy
For Method 3, you can use the following formula to calculate what size squares to cut:
Size of cut square = size of HST unit needed (unfnished size) + ¾in (for seams) x 1.414.
For example, if 31⁄2in HSTs are needed: 3½in + ¾in = 4¼in x 1.414 = 6in. So, cut two 6in squares to begin with.
For example, if 21⁄2in HSTs are needed: 2½in + ¾in = 3¼in x 1.414 = 4.59in (rounded up to 4¾in). So, cut two 4¾in squares to begin with.
METHOD 4: SQUARES SEWN TOGETHER – MAKES 16 UNITS AT ONCE
If you have lots of HST units to make, then making them sixteen at once is faster and more efficient. All units are identical and start of as squares. Final trimming is required.
Calculate what size of squares you need to cut (see Maths Made Easy at the bottom of this section). Cut a square from two different fabrics and place them right sides together, matching all edges exactly. Place the lighter square on top if you can.
Find the exact centre of each side of the top square and mark a line in pencil from side to side and top to bottom, as shown by blue lines in Figure A below. Pin the squares together.
Sew around all four sides 1⁄4in away from the edge, and then sew ¼in from both sides of the marked lines (Fig B above).
Now cut the sewn unit apart on the marked vertical and horizontal lines and also along the diagonal lines shown in Fig C and D. You can make all of the cuts in eight stages if you keep the unit very still as you cut. If it does move, just put it carefully back into place (or cut each square separately if you prefer). When making the diagonal cuts, make sure that your ruler bisects the corners of the squares (Fig E).
Take each unit, open it up and then press the seam open or to one side (Fig F). Check the size of each HST, trimming as needed.
Maths made easy
For Method 4, you can use the following formula to calculate what size squares to cut:
Size of HST unit needed (unfnished size) x 1.414 + ¾in (for seams) x 2.
For example, if 3in HSTs are needed: 3in x 1.414 = 4.24in (41⁄4in)+¾=5in x 2=10in. So, cut two 10in squares to begin with.
For example, if 2in HSTs are needed:
2in x 1.414 = 2.8in (rounded up to 3in) + ¾in = 3¾in x 2 = 7½in. So, cut two 7½in squares to begin with.
METHOD 5: FOUNDATION PIECING – MAKES MULTIPLE UNITS DEPENDING ON UNITS PER TEMPLATE
Foundation paper piecing can be used for really accurate piecing where no trimming is needed. All units are identical. A template for making 2½in (unfinished) HSTs is available (see Templates section), or you could make your own, as described in Creating a Foundation Paper Piecing Template.
Print or copy the full-size template (or as many as needed) onto printer paper, tracing paper or foundation paper.
Cut pairs of fabric rectangles large enough to cover the template with about ½in extra all round. Press the fabric rectangles right-sides together. Put the template on top of the fabrics, right-side up (lines showing). Pin in place
Shorten your machine stitch length to about 1mm and sew along all of the black lines on the template, stitching one or two stitches beyond the lines
Once sewn, remove the pins and press from the fabric side. Using a quilter’s ruler and rotary cutter, cut along all of the blue lines and then all the red lines
On each unit tease away the short line of stitching at the corner and tear away the paper. Press the seam open or to one side. Trim dog’s ears and check the unit is the correct size.
CREATING A FOUNDATION PAPER PIECING TEMPLATE
You can create your own foundation paper piecing (FPP) template to make any size of HST you like. The following example shows a 2¾in square HST unit (unfinished), creating twelve HSTs at once from one sheet of A4 paper. It helps to have fine felt-tip pens in blue, red and black. For this size of HST, six squares will ft on an A4 sheet, which will yield twelve HSTs.
On an A4 sheet of paper draw six squares in a 2 x 3 layout using a blue pen (Fig A above). The size of the squares needs to be the size of the sewn (unfinished) HST you want plus 3⁄8in. So an HST 2¾in + 3⁄8in = 31⁄8in square.
Draw diagonal lines with red pen through the squares following the directions in Fig B above. These red lines and the blue lines will be the cutting lines later. Drawing the lines this way will allow you to sew and cut in the most efficient way (i.e., in long lines).
Draw a second set of diagonal lines this time in black pen 1⁄4in away from the red lines. Note that the 1⁄4in measurement needs to be parallel to the lines, as shown by the little arrows in Fig B above. These lines will be your sewing lines.
When the lines are drawn check that the HSTs will be 2¾in by measuring across the dimensions shown by green lines in Fig B above. Check this in several places. If this measurement is not 2¾in then some of your ¼in sewing lines have not been marked correctly, so check them all again. You will notice that your lines should cross at certain centre points, so check this too.
Trim the sheet down so it is ½in bigger all round than the grouping of squares (Fig C above). Label the template with the size of the HSTs. The template is now ready to be used as a foundation paper piecing template (see Method 5).
Always test a template first on actual fabric before proceeding with a project. If you scan your template into a computer and save the file you will be able to print out as many as you like. This same principle can be used to create templates for smaller sizes of HSTs, varying the directions of the drawn lines as necessary. The figure below shows an example of a template for 1½in (unfinished) HSTs, where the initial squares are drawn at 1 7⁄8in, i.e., the size of unfinished HST needed (1½in) + 3⁄8in.
Example Blocks Using HSTs
Dozens, if not hundreds of blocks use HSTs. Here are some you might like to try. Some blocks are made up of just HSTs, while others have the addition of other units.
HSTs – TROUBLESHOOTING
Here are answers to some of the most frequently asked questions about half-square triangle units.
I’m having trouble with HSTs as quite often the points get cut off.
Try this… There are two main reasons for this. The first reason is that when sewing two HSTs together their triangle points weren’t matched up, so one ends up lower than the other – Fig A shows the correct piecing and Fig B the problem piecing.
The second reason for cut of points is that when sewing a pair of HSTs to another unit the seam allowance available isn’t ¼in, so the stitching line passes through the top of one or both triangles. Fig A shows where the seam needs to be stitched if seams are pressed open and Fig B if seams are pressed to one side.
Whenever you can, try to add the new unit with the HST piecing on top, so you can see the triangle points. Stitch more slowly as you approach the centre point and if you think the seam is going to end up too low or too high then adjust direction slightly to compensate. Below shows the correct piecing and the problem piecing.
I’m following a quilt pattern but a lot of my half-square triangles have ended up smaller than they should be.
Try this… If the units are considerably smaller, say more than ¼in, then there’s not much you can do. You could make all subsequent units for the quilt smaller too, so you end up with a smaller quilt at the end. If the units are only 1⁄8in too small then try re-pressing them with some careful use of steam, which might coax their size out a bit. Failing that, you could remove the stitching and adjust your seam allowance to a narrower one, but this could be time-consuming and fiddly if you have lots of units to ‘fix’. I always make HSTs a ¼in–½in bigger than I need and then trim them down to the correct size. This gives more flexibility and allows for errors in seam sewing. If you use Method 5, making HSTs with paper piecing, this will produce HSTs exactly the size you desire.