Half-Square Triangle Calculator

Get precise cutting sizes for HSTs using the 2-at-a-time or 4-at-a-time method.

Desired Finished HST Size (inches)

Number of HSTs Needed

Reference Table — Common Finished Sizes

Finished Size	Unfinished Size	2-at-a-Time Cut Square	4-at-a-Time Cut Square

How to Use the HST Calculator

Enter the finished size of your HST — the size it will be after sewing into your quilt block (not including seam allowance).
Enter how many HSTs you need total for your project.
Click Calculate to see cutting sizes for both methods and how many squares to cut.

2-at-a-Time Method

Layer two squares right sides together.
Draw a diagonal line from corner to corner.
Sew ¼" on each side of the drawn line.
Cut on the drawn line. Press open. Trim to unfinished size.
Each pair of squares yields 2 HSTs.

4-at-a-Time Method

Layer two squares right sides together.
Draw both diagonal lines (X pattern).
Sew ¼" on each side of both drawn lines.
Cut on both diagonal lines. Press open. Trim to unfinished size.
Each pair of squares yields 4 HSTs (but they will be slightly less accurate than the 2-at-a-time method).

Formula Reference

2-at-a-time cutting size = Finished size + 0.875"
4-at-a-time cutting size = Finished size + 1.25"
Unfinished HST size = Finished size + 0.5"