The Four-at-a-Time “Split” Quarter Square Triangles (Split QST) Calculator

What’s the Math for Four-at-a-Time Split QSTs?

If you want to make Split Quarter Square Triangles (or as I think of it “a QST-HST hybrid”), you can easily make them four-at-a-time. Make your two HSTs. Then grab two (2) squares that are your Finished block size + 1” (the “Split” Square size in the calculator above) and use one of them in place of the second HST (then repeat with the second HST and square to make four Split Quarter Square Triangles).

Note: the only thing to remember with Split QSTs is that half will end up being mirror images of the others!

Before you start, you’re going to need to know two things:

  • The Finished size of your Split-QST (that’s the dimension once it is all sewn together)

  • Whether you want to be exact or have a little extra fabric to trim down to size

The “Exact” Split-QST Formula

If you're making QSTs Two-at-a-Time, you'll need (2) same-size squares of different fabric. The "official" math (or what I call the in-a-perfect-world-where-I-don't-make-mistakes math) states that you add 1¼" to your desired finished size QST and ⅞" to the finished Split-QST size to get the starting size for the Square that will “split” the triangles in two.

Starting Square Size = Finished Split-QST Size + 1¼"

“Split” Square Starting Size = Finished Split-QST Size + ⅞"

The “Oversized” Split-QST Formula

I always trim my QSTs down to size (and I assume you do too): to factor in a little extra room for trimming, just add 1½" to your finished size to get your Starting Square Size and 1" to your finished Split-QST size to get the “Split” Starting Square Size, and you'll be good to go!

Starting Square Size = Finished Split-QST Size + 1½"

“Split” Square Starting Size = Finished Split-QST Size + 1"

How to Make Four-at-a-Time Split HSTs Step-by-Step

"But, how do I make Split-QSTs Four-at-at-Time?" you ask? To start, you are going to need two (2) squares of fabric (measuring the “Starting Square Size in the calculator above).

Step 1: Draw a diagonal line on the back of one of your Starting Squares

Step 2: then place it on top of the other Starting Square, right sides together

Step 3: sew a ¼" on either side of the line then cut along the drawn line and press

Step 4: draw a diagonal line on the back of both of your Split Squares (remember that these do not have to be a different color than the HSTs, it’s just for the purposes of illustration here!)

Step 5: place a Split square on top of each of your HSTs, so that the marked line is perpendicular to the seam of the HST

Step 6: sew a ¼" on either side of the lines then cut along the drawn line

Step 7: press and trim down to size as necessary (to the “Unfinished” size in the calculator above). Note that half the Split-QSTs are mirror images of the other.

What About Other QST Layouts?

Want to make QSTs with two or four fabrics? Make sure to check out the calculators for those via the buttons below: