# Set the length of 1ex

How can I set the length of 1ex? I tried \setlength{1ex}{4.40999pt} but I get errors.

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ex is a font-dependent unit of measurement. See Which measurement units should one use in LaTeX? and What are the various units (ex, in, pt, etc.) expressed in mm? –  percusse Aug 12 '12 at 20:01
... and what exactly do you need it for? Maybe there is some other way than changing 1ex which is really impossible. –  tohecz Aug 12 '12 at 20:12
Are you trying to change the font size? –  Brent.Longborough Aug 12 '12 at 20:16
shouldn't it be enough to set \fontdimen5 to some value? –  topskip Aug 12 '12 at 21:06
@PatrickGundlach You can change a \fontdimen only when the font has just been loaded into memory. With LaTeX it's very difficult unless the font is loaded before \documentclass. –  egreg Aug 12 '12 at 22:26

As already mentioned in the comments: ex is a font dependant value and you change it by changing \fontdimen5:

\documentclass[]{scrartcl}
\usepackage[T1]{fontenc}

\begin{document}
a\hspace{1ex}b

\fontdimen5\font=1cm
a\hspace{1ex}b

\fontdimen5\font=2cm
a\hspace{1ex}b

\bfseries
a\hspace{1ex}b

\normalfont
a\hspace{1ex}b

\large
a\hspace{1ex}b

\small
a\hspace{1ex}b

\end{document}

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