How to Size Half Square Triangles

The ubiquitous half square triangle block. (Often called in HST.) They’re just about unavoidable in quilting, but many do avoid them! There are so many methods for making them and I could easily write a post just on all those methods, but often the reason a quilter would avoid an HST is because you go to all the effort of making them, and then they easily end up wonky and points get lost. It’s really discouraging to do a lot of work for a result that doesn’t look like you wanted! So today I’m going to show you the most consistent way to get accurate, beautiful half square triangles: sizing.

All you need are some HSTs, a cutting board, a rotary cutter, and an acrylic ruler.

1 uncut hst

Unless a pattern already included instructions to “size” your HST, make your HST bigger than the dimensions given in the pattern. An eighth to a quarter of an inch should be plenty of extra. For instance, a lot of patterns make HST by marking the center diagonal across a square, sewing a quarter inch seam on both sides of the line and cutting that apart to make two HST. The measurements for these squares end in the size of the finished block plus 7/8″ which I always round up to make a whole inch. So for this 6″ finished block, I cut a 7″ square instead of a 6 7/8″ square.

2 lined up ready to cut

Place your ruler over the HST so that the diagonal line of the HST matches a 45° angle, and adjust until the whole block fits within the size of the unfinished block with some hanging out all sides as shown. I’m using an Olfa Frosted 12.5″ ruler, and it’s my go-to for sizing because of that diagonal line and great visibility with no slipping. (Not sponsored, I just love the Frosted line so much and am always surprised more people don’t use them.) If your ruler doesn’t have a 45° line to the corner like mine, notice that the inch intersections also line up, and align to that. Aligning the diagonal to the 45° line is what makes for perfect points later.

3 first cuts

Trim the first side, and the top if you feel confident in your cutting skills. If you’re only comfortable trimming one side at a time, turn the HST now to trim the side opposite your first cut, lining up the 45° angle once again.

4 line up

Line up the ruler to the trimmed sides of the HST. If you trimmed the side and top, your HST will look like my picture. If you trimmed the left and right sides, turn to now trim the top and line up the diagonal again. When you trim the bottom, your HST will resemble this picture.

5 last cut

The HST is all trimmed! A perfect 6.5″ square for my 6″ finished block.

The picture in the header of this post is a closeup of the stack of 68 HST I need to press and size. Far from the most I’ve done in one go, but still a little daunting when I look at it! More than anything though, I’m impatient to get through them, because they’re for a quilt I’m designing just for y’all!  Be sure to check out our Instagram for more sneak-peeks and and behind-the-scenes.

Happy creating!


Precise Piecing Tip

Mom and I shopped at garage sales over the weekend and we scored a sentimental treasure. A shoebox of vintage hexagons ready to be pieced and a stack of hexagon blocks caught our eye. As we shifted through the box, looking at all the fabrics, Mom commented that the scrappy assortment of fabrics made this a quilt in the Grandma Mary tradition.

Grandma Mary was my dad’s paternal grandmother, and she’s the one who taught my mom how to quilt. When Grandma Mary made a quilt, she’d throw all the pieces in a basket and pull out each piece without looking. If the pieces clashed, who cared? Scrappy and random was the only way to do it, in Grandma Mary’s opinion. When my parents started dating, Grandma Mary heard my mom could sew, so she asked if my mom knew how to use that “newfangled rotary cutter contraption.” (Sorry to carbon date you like that, Mom!) Before the rotary cutter, all quilters used templates and members of quilt guilds or sewing bees would trade their templates with each other.

In this shoebox, we found a template of Grandma Mary’s. It’s been 22 years since Grandma Mary passed away and she’s still finding her way to us.

1a Happy DiscoveryThese vintage hexagons reminded me of one of my favorite precise piecing tricks. It comes from hand piecing, and you don’t hear much about it for machine piecing because it takes some time and patience, but the results and versatility can be so worth it for those trickier projects.

In hand piecing, one never crosses seam allowances with stitches. Knots at either end completely secure the seam. This hand piecing technique allows quilters to nest every seam as they sew without ever committing a seam to pressing in any given direction. (I know I’ve been guilty of clipping a seam while machine piecing because a seam was pressed the wrong direction for nesting.) It’s also relatively easy to sew challenging angles and Y-seams with hand piecing because of this technique.

1Hand stay stitch collageUsing ¼” quilter’s tape, take a stitch at the corner where the seam allowances meet, and then go back over that stitch to “lock” it.

2 Hand SeamI use a tailor’s stitch, which is a running stitch with a backstitch every inch or so. This makes the seams stronger throughout time. I also took a backstitch at the end before tying off to lock the stitch like I did at the beginning. The seam begins and ends ¼” from the edge of the fabric.

On the machine, there are a few more steps to assure the same level of precision.

3 first pin collageMark your seam allowances on the wrong sides of every piece. Layer the first two pieces right sides together, then use a pin to pierce the fabric at the exact corner where the seams meet. With luck, the pin will come out the other side in the corresponding corner. Just kidding, that never happens! Keep trying until the pin is going through both pieces of fabric at the exact corner. Repeat for the other corner, and for any stabilizing pins.

Quick note on the pins themselves: I’m using Karen Kay Buckley’s Perfect Pins because they are almost excessively thin. I prefer a very, very thin pin for this technique because it’s the least likely to warp the fabric and thus hinder my precision. I’d rather warp a needle than warp my block. Although I’ve had no problem with these pins warping, proof that their name isn’t an unearned brag

4 Stay Stitch collageThis is the trickiest part! Get the fabric under your sewing foot and line your needle up with the first corner pin. Carefully remove the pin and take the first stitch beginning at the exact corner. Reverse and stitch back over the first stitch to “lock” it and then sew along the rest of the seam. Repeat this at the end of the seam by sewing to the exact corner and reversing over the last stitch to lock the seam. Remember to never sew over pins.

6 Finished

So, when is this somewhat time-consuming technique called for? Any Y-seams like in this hexagon block. This technique is a lifesaver when joining sections of a foundation pieced block to ensure all the points match. It can also be the answer to any quilt that needs points to match but is proving impossible using other methods.

Happy creating!