The Four-at-a-Time Half Square Triangles Calculator
What’s the Math for Four-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 Four-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 making HST Four-at-a-Time, you'll need (2) same-size squares of different fabric. While I love this method, I admittedly find the "official" math annoying: take the finished size you need, add a ½" to get the unfinished size, then divide that by .64.
(Finished HST Size + ½") / .64 = Starting Square Size
But, in my opinion, any annoyance caused by the math is made up for in how easy (and quick) it is to make these (no need to draw any lines plus they're a chain piecing dream!).
The “Oversized” HST Formula
And if you want a little extra space for trimming, add a ¼" to the above formula, then round up to the next ⅛" (or ¼" if your ruler doesn't have eighth inch markings or if you simply prefer!).
How to Make Two-at-a-Time HSTs Step-by-Step
"But, how do I make HSTs Four-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: place your two squares right sides together
Step 2: sew a ¼” seam around the border
Step 3: then cut corner to corner
Step 4: press your HSTs and trim down as needed (to the “unfinished dimensions in the calculator above). When pressing, don’t forget that this method does create bias edges, so you want to truly press, and not iron back and forth (pressing will minimize the pulling of the fabric and keep the HSTs from becoming wonky).
Other Ways to Make Your HSTs
If you’re looking to make Two or Eight HSTs at a time, I’ve got the math with step-by-step instructions here: