In electromagnetism, charge density is a measure of electric charge per unit volume of space, in one, two or three dimensions. More specifically: the linear, surface, or volume charge density is the amount of electric charge per unit length, surface area, or volume, respectively. The respective SI units are $C \cdot $, $m^{-1}$, $C \cdot m^{-2}$ or $C \cdot m^{-3}$.