Great "short" answers!
Just to expand into the general concept that will answer this question in a more understandable way:
Wherever you have a macro that expands into a length for instance:
\linewidth, ... Or in this case
\textwidth you can create another length just by setting a floating point factor before the macro.
or in your case
are valid values for the parameter
You can take a look at the first lines of the wiki article: