Editing Area density (section)

{{short description|Mass per unit area}}
{{About|the property of two-dimensional objects|other uses|Density (disambiguation)}}
{{Infobox physical quantity
| name = Area density
| width =
| background =
| image = 
| caption = 
| unit = kg/m<sup>2</sup>
| otherunits =
| symbols = <math>\rho_A</math>
| baseunits = m<sup>−2</sup>⋅kg
| dimension = wikidata
| extensive =
| intensive =
| conserved =
| transformsas =
| derivations = {{ublist|
|<math>\rho_A = \frac {m} {A}</math>
|<math>\rho_A = \rho l</math>
}}
}}

The '''area density''' (also known as '''areal density''', '''surface density''', '''superficial density''', '''areic density''', '''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<sup>−2</sup>). 

In the paper and fabric industries, it is called [[grammage]] and is expressed in grams per square meter (g/m<sup>2</sup>); for paper in particular, it may be expressed as pounds per [[paper ream|ream]] of standard sizes ("basis ream").

A related ''[[area number density]]'' can be defined by replacing mass by [[number of particles]] or other [[countable quantity]], with resulting units of m<sup>−2</sup>.