All lattice planes and lattice directions are described by a mathematical description known as a Miller Index. In the cubic lattice system, the direction [hkl] defines a vector direction normal to surface of a particular plane (hkl). Miller indices are referenced to the crystallographic axes of a crystal. Cubic lattices need only three axes and they correspond to the x, y, z, axes in cubic lattice structures.

Fig.3.6 Intersections of a plane on the x , y and z axis