Accurate Half Square Triangles (HSTs) From Strips

All quilters love half square triangles, right? I sure do, and I just couldn't resist joining a mini-quilt swap this month that is all about half square triangles. I found a colorful jelly roll of V and Co. Ombre fabric by Moda in my stash to use for my mini-quilt, so I thought I would share my method for cutting accurate half square triangles (HSTs) from strips.

Turn Jelly Rolls into HSTs

While you can adapt this method for different size strips and triangles, I actually only use this strip method when I want to make HSTs from jelly rolls. Jelly rolls are convenient packages of pre-cut strips that are 2 1/2" wide by about 40" long. You can easily turn jelly roll strips into 2" finished size HSTs. First sort your strips into pairs that are contrasting values for the two halves of the HSTs. Frequently I will pair a neutral strip with a print or solid color strip. However for this quilt I was being clever with the ombre fabric, so I cut the long strips in half and paired the light ends with the dark ends. Next just sew each pair of strips right sides together with a 1/4" seam along both long edges.

Cut the Strip Pairs into Triangles

You need 2 1/2" unfinished blocks to end up with 2" finished HSTs in your quilt. The extra 1/2" is for the seam allowances when you join blocks together. To begin cutting, place the corner of a ruler on the left end of the strip pair as shown below with the 2 1/2" marks on each side exactly on the bottom seam line. (You lefties probably know to start on the right end.) With most HST cutting methods, I cut oversize and then trim down to the exact unfinished size for the most accurate piecing. However cutting from strips this way is pretty darn accurate, so I can get away with cutting an exact 2 1/2" to start with. There is plenty of room to cut oversize if you prefer cutting HSTs with a safety net. Just place your ruler with the 2 5/8" or 2 3/4" marks on the seam line instead of the 2 1/2" marks. I do recommend marking your placement line on the ruler with washi tape or painters tape. Isn't that pink washi tape fun? It really speeds up the cutting when you can quickly line up the tape on the seam line. After cutting the first triangle, rotate the ruler and put your placement line on the top seam line. Continue rotating the ruler and cutting triangles from the bottom and the top. There will be a small rectangle of waste fabric between each pair of triangles, unless you are lining up your ruler with the corner tip exactly on the opposite seam.

Press and Trim the HSTs

Next open, press, and trim the HSTs. You can either press the seams open or to the side, according to your pattern instructions or your preference. If you made the original cuts oversize you should now square them up to 2 1/2". If you cut them exactly 2 1/2" to begin with you just need to trim off those little dog ears. The outside edges of these HSTs were cut on the bias so handle with care and press them gently to avoid stretching the fabric. A little bit of starch when pressing helps convince those bias edges to behave. I was able to cut ten HSTs from my pair of half strips. The yield will vary depending on the length of the jelly roll strips, how much space you leave between cuts, and whether you oversize the cuts. You will be able to cut between 16 and 20 HSTs from a pair of jelly roll strips.

Play with HST Designs

Once you have trimmed up all of your beautiful little HSTs you can start the fun of sewing them together. These cuties are so versatile with endless design possibilities, which is why I love them so much. I'm not sure where this sample is going, but I will probably add a few more HST friends to make it into a mug rug or place mat.

Want to Make Different Size HSTs?

Yvonne asked in the comments where to find strip sizes to cut different size HSTs. Great question! I generally use this method to make 2" finished size HSTs from jelly roll strips, but you can certainly use it with different size strips. In the table below I have listed what width of strip you would need to be able to cut different size HSTs. The strip widths are rounded up to the half inch to give a little wiggle room in the cutting.
Cheers, Sandy