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, areic density, mass thickness, column density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is the kilogram per square metre (kg·m⁻²). A related area number density can be defined by replacing mass in by number of particles or other countable quantity.

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").