Half Square Triangle Calculator
Enter the finished HST size and how many you need. You get the cut sizes for all three methods.
How the half square triangle calculator works
- 2 at a time: cut squares finished size + 7/8". Draw a diagonal line, sew 1/4" on each side, cut on the line.
- 4 at a time: cut squares finished size × 1.414 + 1 1/4". Sew all the way around, then cut on both diagonals.
- 8 at a time: cut squares 2 × (finished size + 7/8"). Draw both diagonals, sew on each side of them, then cut horizontally, vertically and on the diagonals.
Sizes are rounded up to the nearest 1/8". The 4- and 8-at-a-time methods leave bias edges on the outside, so press gently. Turn on trimming if you like to make them oversized and square up.
Questions
What size square for a 3 inch finished HST?
Cut 3 7/8" squares for the 2-at-a-time method. Add 1/2" (4 3/8") if you want to trim.
What does unfinished size mean?
The size of the HST after you sew it but before it goes into the quilt: finished size plus 1/2". A 3" finished HST measures 3 1/2" unfinished.
Which HST method is most accurate?
2 at a time, because the outside edges stay on the straight grain. The faster methods are fine if you trim each HST to size.