What on earth is a half square triangle? It sounds complicated but if you cut a square in half from the upper left corner to the lower right corner you do get a triangle. So a half square triangle is one that is made from half of a square. But you must remember about seam allowances. If you want to match triangles with the 4 inch squares you made above, you need to start with squares that are 4 7/8 inches on each side; you need a bigger seam allowance because for two triangles will have 6 seams instead of the four seams needed to join for the square. In this diagram the dashed lines represent the seam allowance.

To make a half square triangle, start with squares that are 7/8 of an inch larger than the sides of the triangle that you want. Place your quilting ruler evenly at the upper left and lower right corners of the square and cut the square into two triangles with your rotary cutter. You can stack squares rather than cutting just one at a time.

If you cut the squares and triangles according to the directions given, the two short sides of each triangle will be on the straight grain of the fabric and the long edge will be on the bias. This is the proper layout so that the quilt pieces can come together properly without stretching in the wrong places.



You can see from the diagram that the diagonal cut results in triangle corners that are longer than the needed seam allowance at the upper left and lower right corners of the square. Expert quilters “nub” the corners of triangles, that is cut off the extra fabric at this time. Use the bias square to be precise about cutting off the corners. Put the diagonal line of the bias square at the corner of the triangle and position it so that it precisely measures ½ inch larger than your finished size, 4 ½ inches for our example. Use the rotary cutter to trim off the excess fabric from the points; if you have done everything properly, you should be trimming exactly 3/8 of an inch from each point.