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.
Applicable units are those of quantitykind:ElectricChargeDensity
http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=31891
http://en.wikipedia.org/wiki/Charge_density
http://www.maxwells-equations.com/pho/charge-density.php
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.
$\rho = \frac{dQ}{dV}$, where $Q$ is electric charge and $V$ is Volume.