# Definition:Density (Physics)/Area

< Definition:Density (Physics)(Redirected from Definition:Area Density)

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## 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**.