3×3 Quilt Top Repeater
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Half-Square Triangle
The single most essential building block in quiltmaking
Recolor Fabric Slots
Block Anatomy & Specs
History & Origins of the Half-Square Triangle Block
The Half-Square Triangle (HST) is the fundamental atomic unit of geometric quilting. By joining two right triangles along their hypotenuse, quilters create a square split diagonally into two contrasting colors. HSTs form the foundation for hundreds of classic patterns, including Pinwheels, Sawtooth Stars, Bear Paws, and Jacob's Ladder.
Cutting & Piecing Guide (12" Finished Block)
Precise unit cut sizes and step-by-step piecing instructions.
Choose a finished block size
The cut measurements below update to match.
Piece Cut List
All measurements include a standard ¼" seam allowance. Finished block size: 12".
Step-by-Step Visual Assembly
Place Fabric A and Fabric B squares right sides together.
Draw a diagonal line from corner to corner on the back of the lighter fabric.
Sew 1/4" away from both sides of the marked line.
Cut along the center line and press seams open or toward the darker fabric. Trim unit to size.
Classic Quilt Blocks Built With Half-Square Triangle
The Half-Square Triangle unit is the core building block used in these traditional patterns: