siunitx and missing decimal point

Question

\si seems to be not showing decimal points, unless I specifically specify \num.

\documentclass[12pt]{report}
\usepackage{siunitx}

\begin{document}
\si{12.5\milli\gram}

\si{\num{12.5}\milli\gram}
\end{document}

Is this expected behavior?

Answer 1

The command \si{units} is for units only. You have to use the \SI{number}{units} for what you want to do.

Answer 2

I guess i am replying really late for your query, but you should use \num directly and not nest it in \si.

For a number

\num{12.5}

and \SI (in upper case) for a number with a unit

\SI{12.5}{\milli\gram}