On Fri, Jun 28, 2013 at 8:54 AM, Thomas A. Schmitz <
thomas.schmitz@uni-bonn.de> wrote:

> Hi all,
>
> long story short: I want to calculate a width or height from user input,
> which is in the form "0.x" (as in "0.3\textwidth") since I want to use that
> number differently in different circumstances. Problem is that \dimexpr
> doesn't like decimal values.
>

long answer short
\starttext
\def\myfactor{0.3}
\def\Myfactor{3}
\externalfigure[mill][height=\myfactor\textwidth]
\externalfigure[mill][height=\dimexpr \textwidth * \Myfactor / 10\relax]
\externalfigure[mill][height=\dimexpr 10cm * \Myfactor / 10\relax]
\stoptext
http://wiki.contextgarden.net/Expressions
-- 
luigi