The function GetDimension(dim) returns the argument for a base dimension, and the product of powers of base dimensions for any other dimension.

$\mathrm{with}\left(\mathrm{Units}\right)\:$

Automatically loading the Units[Simple] subpackage

$\mathrm{GetDimension}\left('\mathrm{length}'\right)$

$\mathrm{length}$

$\mathrm{GetDimension}\left('\mathrm{speed}'\right)$

$\frac{\mathrm{length}}{\mathrm{time}}$

$\mathrm{GetDimension}\left('\mathrm{acceleration}'\right)$

$\frac{\mathrm{length}}{{\mathrm{time}}^2}$

$\mathrm{GetDimension}\left('\mathrm{surge}'\right)$

Error, (in Units:-GetDimension) a dimension with name `surge` does not exist

$\mathrm{AddDimension}\left('\mathrm{surge}'=\frac{'\mathrm{length}'}{{'\mathrm{time}'}^3}\right)$

$\mathrm{GetDimension}\left('\mathrm{surge}'\right)$

$\frac{\mathrm{length}}{{\mathrm{time}}^3}$