I did a search on Bonnie Hunter's Quiltville site. She says the formula for quarter sq triangles is add 1 1/4 inches to FINSHED size. You cut that square diagonally twice getting 4 triangles. This put the straight of the grain on the long edge of the triangle- taking the bias away from the edges.
Here is the page...you will need to scroll down into this tutorial till you see ****Formula Hint****
http://quiltville.blogspot.com/2005/...hio-stars.html
Hope this helps!