# dimension command

## Syntax

``` LAMMPS
dimension N
```

-   N = 2 or 3

## Examples

``` LAMMPS
dimension 2
```

## Description

Set the dimensionality of the simulation. By default LAMMPS runs 3d
simulations. To run a 2d simulation, this command should be used prior
to setting up a simulation box via the [create_box](create_box) or
[read_data](read_data) commands. Restart files also store this setting.

See the discussion on the [Howto 2d](Howto_2d) page for additional
instructions on how to run 2d simulations.

:::: note
::: title
Note
:::

Some models in LAMMPS treat particles as finite-size spheres or
ellipsoids, as opposed to point particles. In 2d, the particles will
still be spheres or ellipsoids, not circular disks or ellipses, meaning
their moment of inertia will be the same as in 3d.
::::

## Restrictions

This command must be used before the simulation box is defined by a
[read_data](read_data) or [create_box](create_box) command.

## Related commands

[fix enforce2d](fix_enforce2d)

## Default

``` LAMMPS
dimension 3
```