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HST Calculator — Half-Square Triangles, Flying Geese & Quilt Shapes

Get precise cut sizes and fabric requirements for the most common quilt shapes. Calculate half-square triangles (HSTs) using the 2-at-a-time or 4-at-a-time method, quarter-square triangles (hourglasses), flying geese units, and basic squares — all with correct seam allowances built in.

Shapes & HST

Calculates cut sizes and seam allowances for the most common quilt shapes. "Finished size" is the measurement in the completed, sewn quilt.

All calculations show the exact fabric needed based on your inputs — they do not include extra for cutting errors. Consider adding 5–10% to any yardage figure. Standard quilting cotton WOF is 44".

How It Works

  • Square: finished size + ½\" for seam allowances
  • HST 2-at-a-time: finished size + ⅞\" — draw diagonal, sew ¼\" on each side, cut to yield 2 HSTs
  • HST 4-at-a-time: 2 × finished size + ½\" — sew both diagonals, cut to yield 4 HSTs per pair
  • Quarter-square triangle: finished size + 1¼\" — cut on both diagonals to yield 4 QST units per pair
  • Flying geese: goose rectangle = (width + ½\") × (height + ½\"); sky squares = height + ½\"

Frequently Asked Questions

What is a half-square triangle (HST)?
A half-square triangle block is a square unit made from two right triangles of different fabrics. HSTs are one of the most versatile building blocks in quilting — they're used in dozens of traditional patterns including pinwheels, flying geese, chevrons, and stars.
What is the difference between HST 2-at-a-time and 4-at-a-time?
The 2-at-a-time method pairs two squares, draws one diagonal line, sews ¼" on each side of the line, and cuts along the line to yield 2 HST units. The 4-at-a-time method uses larger squares, draws both diagonals, sews on each side of each line, and cuts to yield 4 HSTs — more efficient when you need many identical units.
What are flying geese units?
Flying geese are rectangular quilt units made of one large center triangle (the "goose") pointing upward, flanked by two smaller corner triangles (the "sky"). They are typically twice as wide as they are tall and are often used in borders or as directional design elements.
What is a quarter-square triangle (QST) or hourglass block?
A quarter-square triangle block is made from four right triangles arranged into a square that looks like an hourglass or bow tie. You cut a large square diagonally in both directions to yield 4 triangles. Two different fabrics create the alternating hourglass design.

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