Area density

Area density
Common symbols	${\displaystyle \rho _{A}}$
SI unit	kg/m2
In SI base units	m−2⋅kg
Derivations from other quantities	${\displaystyle \rho _{A}={\frac {m}{A}}}$ ${\displaystyle \rho _{A}=\rho l}$
Dimension	${\displaystyle {\mathsf {L}}^{-2}{\mathsf {M}}}$

The area density (also known as areal density, surface density, superficial density, column density, or density thickness) of a two-dimensional object is defined as the quotient of mass by area. The SI derived unit is the "kilogram per square metre" (unit symbol kg·m⁻²).

In the paper and fabric industries, it is called grammage and is expressed in grams per square meter (g/m²); for paper in particular, it may be expressed as pounds per ream of standard sizes ("basis ream").

A generalized areic quantity is defined as the quotient of a generic physical quantity by area, such as surface charge density or areic electric charge. A related area number density can be defined by replacing mass by number of particles or other countable quantity.