Iron adopts a body center, cubic units self. Illustrate how the number of atoms per unit cell for the iron atoms are obtained. So remember for any cubic unit, So we have 1/8 atom for every corner, and that's shared between eight atoms. So for all of them it's one atom right off the bat. But remember for a body centered cubic units. Now we also have an additional atom within the center of our cube, so we add that in. So taking those both into consideration, that's how we come up with two atoms per one unit cell for a body centered cubic unit self.