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Half-Square Triangle (HST) Calculator

Find your cut square size, number of squares to cut, and fabric yardage for HSTs.

1 HST Settings

2-at-a-time
8-at-a-time

2-at-a-time method

Fabric A | Fabric B Draw diagonal Cut on diagonal ___________ ___________ ___________ /\ /\ | || | | / | / \ / \ | || | -> | / | -> \ / + \ / |___________| ___________| |___/_____ | \/ \/ 2 HSTs from 1 pair

Place one Fabric A square and one Fabric B square right sides together. Draw a diagonal line on the lighter fabric. Sew 1/4" on both sides of the line. Cut on the drawn line. Press open. Each pair yields 2 HSTs.

8-at-a-time method

Large A Large B Draw X diagonals Sew, cut, press ___________ ___________ 8 HSTs per pair | \ / | | \ / | | \ / | + B -> | X | -> 8 HSTs | / \ | | / \ | |__/_____\__| |__/___\__|

Use squares cut at finished size × 2 + 7/8". Draw both diagonals on the lighter fabric. Sew 1/4" on each side of both drawn lines (4 seam lines total). Cut on both diagonals and both horizontal/vertical center lines. Press open. Each pair yields 8 HSTs.

Trimming to size

Even with precise cutting and sewing, HSTs often come out slightly off-size. Use an HST ruler or a square ruler with a diagonal line to trim each HST to exact finished size + 1/2" (unfinished). Trimming takes time but results in a flat, accurate quilt top.