Half-Square Triangle Calculator
Find the exact cut size for your HSTs — or calculate the finished size from a cut square. Covers both the 2-at-a-time and 4-at-a-time methods.
What finished HST size do you want?
Results
Reference table — common finished HST sizes
| Finished HST | 2-at-a-time cut | 4-at-a-time cut | HSTs from 1 yd (44" WOF) |
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The 2-at-a-time method
Layer two squares right-sides together, draw a diagonal line, sew ¼" on both sides of the line, then cut along the line. You get 2 HSTs. The formula is: cut size = finished size + ⅞".
The 4-at-a-time method
Layer two squares, sew around all four edges (¼" seam), cut diagonally in both directions (an X cut). You get 4 HSTs. The formula is: cut size = finished size + 1¼". The 4-at-a-time method is faster for large quantities but requires precise cutting.
Tips for accurate HSTs
Always press seams open or to the dark side to reduce bulk. Trim each HST to the exact cut-unfinished size (finished + ½") using a square ruler with a diagonal line. This removes the "dog ears" and ensures precision.