# Prefix with no unit with siunitx

How can I typeset a number with a prefix but without a unit with siunitx? The following code

\SI{1.0}{\mega}


gives this error: "Prefix with no unit."

• Of course it does: you can't have 'one mega', only 'one mega <something>'. What is the aim here? – Joseph Wright Nov 19 '14 at 17:21
• I have a table with a column called "number of nodes", and I would like to write "1M" in one of the cells. – jalalhugo Nov 19 '14 at 17:24
• @jalalhugo That's 1×10⁶ – egreg Nov 19 '14 at 17:26
• I understand that "1M" goes against the standard, but ultimately I think that the notation should be at the discretion of the user, so in my opinion raising an error (as opposed to a warning) is pushing it. – jalalhugo Nov 20 '14 at 14:59
• @jalalhugo I agree. It should be only a warning. I'm also using it when discussing unity conversion to teach a trick to convert a number from \meter\squared to \deca\meter\squared: \meter\squared = \frac{\da\squared\meter\squared}{\da\squared} = \frac{\deca\meter\squared}{100}. – Leonardo Castro Jan 27 '16 at 14:28

You can of course do it:

\documentclass{article}
\usepackage{siunitx}

\DeclareSIUnit{\nothing}{\relax}

\begin{document}
\SI{1.0}{\mega\nothing} is a wrong way to typeset data.
\end{document}


However, you should think at least twice whether this is a good way to express yourself and your readers will understand what you mean. With

\num{1e6}


the printout would be much clearer and not so wider.

• This is a perfectly reasonable way to express oneself in some fields. – Reid Sep 1 '16 at 20:29