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Quarter-Square Triangle Calculator

Find the square size to cut for quarter-square triangles from the finished size and seam allowance, and how many squares make the QSTs you need.

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What size squares do I cut for 4" quarter-square triangles?

For quarter-square triangles that finish at 4" with a 1/4" seam allowance:

You enter

Finished QST size
4" (10.16 cm)
Seam allowance
1/4" (0.64 cm)

You get

Cut squares
5-1/4" × 5-1/4" (13.4 cm)
Unfinished size
4-1/2" (11.4 cm)

The formula: cut size = finished size + 4 × seam allowance + 1/4" (metric: + 0.635 cm).

Frequently asked questions

  1. What size squares do I cut for quarter-square triangles?

    Add 1-1/4" to the finished size when you sew a 1/4" seam — a 4" finished QST starts from 5-1/4" squares. A QST has two diagonal seams, so it needs more extra fabric than a half-square triangle. The general rule is finished size + 4 × seam + 1/4".

  2. How many quarter-square triangles do two squares make?

    Two, with the two-at-a-time method: sew the pair of squares into two half-square triangles, layer those with opposite colors facing, sew across the other diagonal, and cut — you get two hourglass QSTs. For N QSTs, cut N squares (rounded up to an even number), half from each fabric.

  3. What is the difference between a half-square and a quarter-square triangle?

    A half-square triangle splits a square into two triangles along one diagonal. A quarter-square triangle (an hourglass unit) splits it into four triangles along both diagonals, so it needs a larger starting square for the same finished size.

  4. Should I cut QST squares oversized and trim?

    Yes, many quilters do: add about 1-1/2" instead of 1-1/4" to the finished size, then trim each unit to the unfinished size after pressing. The two bias seams in a QST make trimming especially worthwhile.

  5. Which way should I press quarter-square triangle seams?

    Press the first seam toward the darker fabric so the seams nest when you pair the units, then press the final diagonal seam open to reduce bulk at the center point.

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