# Definition:Density (Physics)/Area

## Definition

The area density of a two-dimensional body is its mass per unit area.

The usual symbol used to denote area density is $\rho_A$, although some sources simply use $\rho$ if the context makes it clear that it refers to area density rather than volume density.

Occasionally, $\sigma$ (Greek letter sigma) is also used, but this is more commonly used for surface charge density.

### Dimension of Area Density

The dimension of area density is $M L^{-2}$: mass per unit area.

### Units of Area Density

Thus:

$1 \ \mathrm g \ \mathrm{cm}^{-2} = 10 \ \mathrm{kg} \ \mathrm m^{-2}$

## Also known as

Also known as surface density, areal density or planar density.