For the setting triangles, which I think is what you are asking, you need 4half square triangles...one for each corner, but the 4 sides need quarter square triangles to eliminate the bias edge...I am not where I can get the exact formula, but I think for the QST you need to cut block 2" larger than your pieced block then cut into an X, thus getting 4 triangles. I am sure somewhere on line there is a cutting table available.