Quarter-square triangle (QST) chart
The unit behind Ohio Star, hourglass blocks and every quilt edge that needs to stay straight. Cut sizes, the formula, and why the allowance is bigger than an HST.
A quarter-square triangle comes from a square cut twice on the diagonal, giving four triangles whose long edge is on the straight grain. That is the whole reason the unit exists: put a QST on the outside edge of a block and the edge will not stretch, where an HST in the same spot puts bias on the block's perimeter.
QST cutting chart
| Finished unit | Cut square | Unfinished (trim to) |
|---|---|---|
| 1" | 2¼" | 1½" |
| 1½" | 2¾" | 2" |
| 2" | 3¼" | 2½" |
| 2½" | 3¾" | 3" |
| 3" | 4¼" | 3½" |
| 3½" | 4¾" | 4" |
| 4" | 5¼" | 4½" |
| 4½" | 5¾" | 5" |
| 5" | 6¼" | 5½" |
| 6" | 7¼" | 6½" |
| 7" | 8¼" | 7½" |
| 8" | 9¼" | 8½" |
| 9" | 10¼" | 9½" |
| 10" | 11¼" | 10½" |
| 12" | 13¼" | 12½" |
The formula
Finished size + 1¼″. That is ⅜″ more than the ⅞″ used for a half-square triangle, and the extra covers the second bias cut — a QST has bias on two sides where an HST has it on one.
QST or HST?
They look similar and behave very differently:
| Half-square triangle | Quarter-square triangle | |
|---|---|---|
| Cut from one square | Once on the diagonal | Twice on the diagonal |
| Triangles per square | 2 | 4 |
| Straight grain on | The two short legs | The long edge |
| Cutting allowance | ⅞″ | 1¼″ |
| Best used | Anywhere inside a block | On block edges, and for sharp star points |
Making an hourglass unit
- Make two oversized half-square triangles from squares cut 1¼″ larger than the finished unit.
- Layer them right sides together with opposite fabrics facing and the diagonal seams nesting.
- Draw a diagonal perpendicular to the existing seams, stitch a quarter inch either side, and cut apart.
- Two hourglass units, with all four points meeting cleanly at the centre.
This crossed-HST method is more accurate than cutting four loose triangles and reassembling them, because the bias never gets handled loose.
Pressing
Four seam allowances meet at the centre of a QST unit. Press that final seam open — it is one of the few places where open pressing is clearly better, because a side-pressed centre creates a lump that no amount of quilting will flatten.
Ohio Star → · Hourglass → · HST chart →
Questions
What size square do I need for a 6 inch finished quarter-square triangle?
Cut the square at 7¼ inches — the finished size plus 1¼ inches. One square cut twice on the diagonal gives four triangles.
What is the difference between a QST and an HST?
An HST is a square cut once diagonally, giving two triangles with straight grain on the short legs. A QST is cut twice, giving four triangles with straight grain on the long edge, so it can sit on a block edge without stretching.
Why is the quarter-square triangle allowance 1¼ inches?
It covers two bias cuts rather than one. A half-square triangle only needs ⅞ inch because it has a single diagonal.
Stop looking things up
FourPatch does this arithmetic for every piece in your quilt, every time you change something — block size, sashing width, fabric width, waste allowance. The cutting list and yardage just update.