Quilt QST Calculator: Quarter-Square Triangle Cut Size and Squares

Work out QST cut size before you cut. Enter finished QST size and QSTs needed, and see cut square size, squares per fabric, total squares and QSTs made, with the formula in steps.

Calculate your QST cut size

Finished QST size in

QSTs needed

QSTs needed is a whole number, greater than zero. Count QSTs by fabric pair, not by quilt, if different fabric pairs use different finished sizes.

This calculator uses the two square method only. Each set of 2 squares makes 4 QSTs.

This calculator uses the two-square method only. Two squares, one of each fabric, sewn on both diagonals and cut on both diagonals, make 4 QSTs. For half-square triangles, use the HST Calculator, or the Fabric Calculator for fabric yardage.

Your result

Enter your measurements, then calculate.

How the calculator works

Step 1: Cut square size

Cut square size equals finished QST size plus 1 and 1/4 inches, which is 1.25 inches, for the two-square method. The extra 1.25 inches covers seam allowances on the diagonal seams and trimming to finished size. For finished QST size 4 inches, cut square size equals 4 plus 1.25, equals 5.25 inches.

Step 2: Sets needed and squares per fabric

Sets needed equals QSTs needed divided by 4, rounded up to a whole number, because each set of 2 squares makes 4 QSTs, and a partial set cannot be sewn. For QSTs needed 20, sets needed equals 20 divided by 4, equals 5 sets. Squares per fabric equals sets needed times 1, because each set uses 1 square of each fabric. For sets needed 5, squares per fabric equals 5 squares.

Step 3: Total squares and QSTs made

Total squares equals squares per fabric times 2, because each set uses one square of each fabric. For squares per fabric 5, total squares equals 5 times 2, equals 10 squares. QSTs made equals sets needed times 4, because each set makes 4 QSTs. For sets needed 5, QSTs made equals 5 times 4, equals 20 QSTs, exactly the number needed, with no extra QST.

Assumptions, shown next to the result

This calculator uses the two-square method only, with seam allowance 0.25 inch on each side, as is standard for piecing. Cut square size is used as entered in the unit mode you choose, with no extra added for mistakes or shrinkage, beyond the 1.25 inches already in the formula. If QSTs needed is not a multiple of 4, sets needed is rounded up, and QSTs made will be more than QSTs needed, which is extra QSTs, not a mistake.

QST cut size chart

This chart uses the same formula as the calculator: cut square size equals finished QST size plus 1 and 1/4 inches, which is 1.25 inches, for the two-square method.

Finished QST size	Cut square size
2 inches	3.25 inches
3 inches	4.25 inches
4 inches	5.25 inches
6 inches	7.25 inches
8 inches	9.25 inches

Chart values are a guide for the finished sizes shown. Your own finished size may give a different result. Use the calculator above for your own measurements.

Worked example, checked against the calculator

Finished QST size 4 inches, QSTs needed 20.

Cut square size: 4 plus 1.25 equals 5.25 inches.

Sets needed: 20 divided by 4 equals 5 sets.

Squares per fabric: 5 times 1 equals 5 squares per fabric.

Total squares: 5 times 2 equals 10 squares.

QSTs made: 5 times 4 equals 20 QSTs, exactly the number needed, with no extra QST.

Frequently asked questions

How do I calculate quarter-square triangle cut size?

For the two-square method, cut square size equals finished QST size plus 1 and 1/4 inches, which is 1.25 inches. For example, a 4 inch finished QST needs 5.25 inch cut squares.

What is a quarter-square triangle?

A quarter-square triangle, or QST, is a square made from four triangles, sewn together on the diagonals, usually with two different fabrics in an hourglass layout. Its finished size is the size in the finished quilt, after seams are sewn.

How many squares do I need for QSTs?

For the two-square method, each set of 2 squares, one of each fabric, makes 4 QSTs. Sets needed equals QSTs needed divided by 4, rounded up to a whole number. For example, 20 QSTs need 5 sets, 5 squares per fabric, 10 squares total, and make 20 QSTs exactly.

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