Quarter Square Triangle (QST) Calculator
Zero Waste & No Sign-up: Calculate cutting sizes for Quarter Square Triangle (QST) blocks. Get exact square sizes for both 2-at-a-time and 4-at-a-time methods.
How to Use the QST Calculator
Enter the finished size of your quarter square triangle (hourglass) unit. The starting square is cut at the finished size plus 1-1/4 inches — a 4-inch finished unit starts from a 5-1/4 inch square — then cut on both diagonals to yield four triangles.
Hourglass units combine triangles from two contrasting squares, and each starting square contributes enough triangles for two finished units. The calculator therefore reports squares needed as the unit count divided by two, rounded up, for each fabric pairing.
The extra 1-1/4 inch exists because both seams cross the square on the bias diagonal. The double diagonal cut also places the straight grain on the long outer edge of each triangle, which is exactly where you want stability — the finished hourglass ends up with no bias on its outside edges. If you need many hourglass units from the same two fabrics, cut the starting squares in matched pairs and chain-piece them — the squares-needed math holds at any batch size.
Frequently Asked Questions
What is a Quarter Square Triangle (QST)?
A QST, also called an hourglass block, is made by cutting a square diagonally in both directions to produce four right triangles. Two contrasting fabrics are sewn together to create the hourglass effect.
What is the formula for QST cutting size?
Add 1-1/4 inches to the desired finished size. For a 4-inch finished QST, cut a 5-1/4 inch square and cut diagonally twice to yield four quarter-square triangles.
What is the difference between HST and QST?
An HST (Half Square Triangle) is cut once diagonally to make two triangles. A QST is cut twice diagonally to make four triangles. QSTs have the straight grain on the longest edge, while HSTs have it on the short edges.