Definition:Density (Physics)/Area

Definition

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

Symbol

The usual symbol used to denote area density is $\rho_A$ (Greek letter rho), 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

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

Units

• The SI units of area density are $\mathrm {kg} \ \mathrm m^{-2}$ (kilograms per square metre).

• The CGS units of area density are $\mathrm g \ \mathrm{cm}^{-2}$ (grams per square centimetre).

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.

Also see

• Definition:Density (Physics)
• Definition:Linear Density