Quarter-Square Triangle (QST) Quilt Block
Four triangles meeting at the center — the essential unit for star points, hourglasses, and pinwheels
The quarter-square triangle unit contains four right triangles meeting at the center — essentially two half-square triangles sewn together on the remaining diagonal. It's the unit that makes Ohio Stars, Hourglass blocks, and hundreds of other classic patterns possible.
History & Background
The quarter-square triangle is not typically named as a distinct block — it's a construction unit, the building block behind dozens of named patterns. Wherever you see a square divided into four triangles (the Hourglass, the X block, the X-and-Plus), you're looking at quarter-square triangle construction.
As a practical technique, QSTs emerged as quilters became more systematic about using right-triangle geometry to create complex patterns without set-in seams. The two-step process — make HSTs, then sew two HSTs together on the remaining diagonal — was documented in quilting texts by the mid-19th century and became standard practice by the 1880s.
The most important modern application is in star blocks. The Ohio Star's eight crisp points are created by four QST units, each contributing two triangle halves to adjacent star points. The technique for making QSTs from squares (the "2-at-a-time HST then QST" method) is now one of the most important precision skills in quilting — it appears in patterns at every level of complexity.
Step-by-Step Instructions
Start with two HSTs
Make two half-square triangle units using your chosen fabrics. For a 4" finished QST, cut squares at 5¼" — the QST formula is finished size + 1¼" (not the HST formula of +⅞"). Make two HSTs at this size.
Pair the HSTs
Place two HSTs right-sides-together with opposite fabrics touching (light against dark). The diagonal seams should run in opposite directions. They will nest cleanly for accurate sewing.
Draw and sew the second diagonal
Draw a diagonal line perpendicular to the existing seam (from corner to corner, crossing the seam). Sew ¼" on each side of this new line.
Cut and press
Cut on the drawn diagonal. Press seams open. You now have two QST units from each pair of HSTs.
Trim to finished size
Use a square ruler to trim each QST to the exact size needed. A QST for a 12" Ohio Star should be trimmed to 4½" (finished 4"). Line up the diagonal line on your ruler with the center seam intersection.
Tips & Techniques
- Press QST seams open rather than to one side — the center intersection has four seams meeting, and open seams distribute the bulk evenly.
- The sizing formula for QSTs: finished size + 1¼" = cutting size for the initial squares. This accounts for two diagonal cuts.
- Always trim QSTs after pressing. Even a ⅛" error in a QST will cost you your star points.
- The most common error: making the HSTs too small so the QST can't be trimmed to the correct size. Cut your initial squares generously and trim down.
Color & Fabric Selection
QST units are usually paired — two of the same unit appear in each pattern position. Keep this pairing in mind when choosing fabrics: the unit that becomes the star point should use two colors that create visual contrast both within the unit and against the neighboring units.
Variations & Related Patterns
Hourglass Block
Four QST units assembled into a square, creating an hourglass or bowtie shape.
Ohio Star Points
The most common use of QSTs in traditional quilting — four QST units forming the eight points of an Ohio Star.
X Block
QST units arranged to create an X or plus-sign shape depending on color placement.
Quick Facts
Put it to use
NiftyFifty quilters have been swapping blocks like this one since 1997. Browse our historical archive or join a new swap.
Browse quilt swaps →Related Guides
Ohio Star Quilt Block
IntermediateEight crisp star points emerge from four quarter-square triangle units — a pattern that rewards precise piecing
Half-Square Triangle (HST) Quilt Block
BeginnerThe most versatile unit in patchwork — master this and you can make hundreds of different quilt patterns
Sawtooth Star Quilt Block
IntermediateFour flying geese units form four star points around a center square — a step up from Ohio Star in visual complexity