How to Cut Quarter-Square TrianglesQuarter-square triangles look just like half square triangles, but they're very different. The straight fabric grain runs along the longest edge of a quarter-square triangle, while it runs along the short edges of half-squares.
Quarter-square triangles are used in several ways, but most often as setting triangles, where they fill in the jagged edges surrounding blocks arranged on point. That configuration puts their long, straight grain edges on the perimeter of the quilt.
Using half square triangles in that position would result in a quilt with stretchy bias edges on its perimeter, not a good thing since you want quilt edges to stay as intact as possible while you're finishing up.
Cutting Quarter-Square Triangles
- Cut a square with sides that are 1-1/4" longer than the finished length of the triangle's longest edge.
- Use your rotary equipment to cut the square in half twice diagonally.
Cutting Setting Triangles
- Finished block size x 1.41 = finished length required on the triangle's longest edge. Round up to nearest 1/8".
- Cut a square with sides that are 1-1/4" longer than the number in Step 1.
- Cut the square in half twice diagonally.
Commonly Used Setting Triangles
- 6" blocks: cut four triangles from a 9-3/4" square
- 9" blocks: cut four triangles from a 14" square
- 10" blocks: cut four triangles from a 15-3/8" square
- 12" blocks: cut four triangles from a 18-1/4" square