The formula of copper oxide depends on whether it is copper(I) oxide or copper(II) oxide. Both compounds contain copper and oxygen, but one has a greater ratio of copper to oxygen than the other.
Copper(I) oxide has a formula of Cu2O. This means each molecule of copper(I) oxide has two atoms of copper and one atom of oxygen. This compound is also known as cuprous oxide. Copper(II) oxide has a formula of CuO. Every molecule of this compound has a one-to-one ratio of copper to oxygen. Copper(II) oxide is also called cupric oxide. Both forms of this compound have applications in the manufacturing and agricultural industries.