A quarter square triangle (QST) is formed when both of a squares diagonals are cut to form four equal triangles. Each triangle formed is a right angle triangle. The straight of grain is on the hypotenuse. A QST looks like a half square triangle (right angle triangle with two equal sides). The difference between the two is where the bias is placed. The bias on a QST falls on the two shorter sides of the triangle. The bias of a half square triangle (HST) falls on the longest side.
In the photo above, the white triangles in the corners are HST’s. They work best in the corner because the straight of grain falls on the outside edges which helps keep the block flat. The red star points, grey section between the points and the white triangles in the middle are QST’s. The straight of grain of the grey triangles also falls on the outside edge of the block.
There are many ways to make QST. Most people prefer rotary cutting rather than using templates. To rotary cut these triangles, you will need to find the finished size of the triangle (length of the longest side). The “formula” (listed below) works like a charm every time.
- Measure the FINISHED SIZE of the HYPOTENUSE side of the triangle.
- Add 1 ¼ inches to the FINISHED SIZE of the HYPOTENUSE side of the triangle.
- Cut out a square measuring FINISHED SIZE of HYPOTENUSE side of the triangle plus 1 ¼ inches.
- Cut the square on both diagonals.