The formula for cutting setting triangles is:
Finished Block size x 1.414
Round to nearest 1/8”
Add 1-1/4”
Cut out and quarter the block
If your finished square is 8", 8x1.414 = 11.312 rounded to nearest 1/8 would be 11.375, plus 1.250 = 12.625 (12-5/8). Cut corner to corner and you have 4 side setting blocks and the outside edge is not on the bias.