Updated: Jun 8
Personally, I used to hate sewing half-square triangles (HSTs). There are some beautiful quilt patterns made almost exclusively from them, but the thought of sewing then trimming 400+ HSTs one-by-one sounded like agony. You could always just not trim them, but then matching points becomes almost impossible. That's when I discovered HSTs by the strip. While this method has been around for a while, it has never become super popular. Why? I have no idea because I think it's amazing! Rather than cutting squares and sewing diagonals like you would in a two-, four-, or eight-at-a-time method before cutting them apart, pressing, and trimming AGAIN, you just cut strips and then cut those strips into perfect HSTs. No trimming is necessary. They come out perfectly sized and perfectly precise.
Here's How it's Done
1. First, cut your strips. The chart below lists some common sizes and the corresponding width of the strip you need. For the purpose of this tutorial, I'm going to be making HST units with a finished size of 2.5" inches and an unfinished size of 3" so I'm using some 2.5" wide jelly roll strips.
2. Match right sides together and sew your 1/4" seam down both sides of the strip to form a strip tube.
3. Align the 45 degree line on your ruler with one of the edge seams and make a cut against the ruler to put the initial 45 degree angle on the end of your strip tube.
4. Find the unfinished size mark on each side of one of the corners of your ruler. Since my unfinished HST size is 3", I'm finding the 3" mark on each edge. Place a piece of masking or washi tape diagonally across the corner of your ruler. spanning the 3" mark (or whatever unfinished size you are making).
NOTE: You can help align your tape better by checking to make sure that it crosses each of the intermediate 1" cross-hair markings on your ruler since it should be at exactly a 45 degree angle.
5. Now this is the magic - Align the masking tape on the corner of your ruler with the seam on one edge of your strip tube. The edge should align with the 45 degree cut you made previously on one end of the strip tube. Make cut against ruler forming an HST.
6. Flip the strip tube around and repeat the process aligning the masking tape to the seam and making a cut.
7. Open the HST units pressing your seams according to your preference. You may have a stitch or two remaining at the apex of the HST unit. Just pop it gently. It should come out very easily. Viola! Perfect HSTs with only one round of cutting and sewing.
Here's why I love this method so much
By aligning the ruler to the seam rather than the edge (which is neither always straight nor always exactly 1/4"), you ensure that the seam stays precisely in the corner of your HST rather than getting shifted to one side or the other. Additionally, since you use your ruler to determine the size of the unfinished HST, there's no funky math or 1/8" increments to deal with. As long as you are careful not to distort the HST during pressing, the units come out darn near perfect every single time. It's so fast!
The only drawback to this method is that it results in all bias edges around your HST unit. To be fair though, the four-at-a-time method does too; only the two-at-a-time and eight-at-a-time methods do not. I sew so many biased edges these days that this doesn't bother me at all and I think most modern quilters are this way. (Check out my precision piecing for lazy quilters series if you want to learn some easy things to make sewing bias edges easier.) The only quilt pieces that don't result in bias edges are basically rectangles and those are no fun. For me, the tradeoff of a bias edge is more than worth it to avoid trimming. I'll never go back!
Ready to give it a try? You can download the free PDF instruction sheet below. It contains illustrated instructions, an expanded cutting chart, as well as the equation for calculating the initial strip width for any sized HST. This method is also used in my quilt pattern, Seud Medallion, along with a few other tricks to make an otherwise complicated pattern, quick and easy.