The Two-at-a-Time Half Square Triangles Calculator
What’s the Math for Two-at-a-Time HSTs?
Curious about what’s going on “under the hood” of the calculator? Like to do the math out longhand? Here’re the calculations for making HSTs Two-at-a-Time.
Before you start, you’re going to need to know two things:
The Finished size of your HST (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” HST Formula
If you're using the Two-at-a-Time HST method, you'll need two 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 ⅞" to your desired finished size HST:
Finished HST Size + ⅞" = Starting Square Size
The “Oversized” HST Formula
I always trim my HSTs down to size (and I assume you do too). The rule of thumb to have enough wiggle room to trim is to just add 1" to your finished size (or a ½" to your unfinished HST) and you'll be good to go!
Finished HST Size + 1" = Starting Square Size
How to Make Two-at-a-Time HSTs Step-by-Step
"But, how do I make HSTs Two-at-at-Time?" you ask? Don't worry, it's easy! 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 squares
Step 2: then place it on top of a background square right sides together
Step 3: sew a ¼" on either side of the line then cut along the drawn line
Step 4: press and trim down to size as needed (the “unfinished” dimensions in the calculator above).
Other Ways to Make Your HSTs
If you’re looking to make Four or Eight HSTs at a time, I’ve got the math with step-by-step instructions here: