How to create fractional SI units (\SI{…}{\sqrt{s}})?

Question

I want to express a variable that has "square root units", i.e. 0.8e-3 m/sec^1.5.

I have tried to use the SI package:

\SI{0.8e-3}{\radian\per\second\sqrt{\second}}

However, this does not work. It only works in cases like this:

\SI{42}{\second}

Is there a good way of expressing "square root units" or similar? Or is it necessary to use a workaround like:

\num{0.87e-5}\,$\mathrm{m}/\mathrm{s}\sqrt{\mathrm{s}}$

Answer 1

Arbitrary powers can be given using \tothe:

\documentclass{article}
\usepackage{siunitx}
\begin{document}

\SI[per-mode = symbol]{0.87e-5}{\metre\per\second\tothe{1.5}}

\end{document}