# Big O symbol (order of) and siunitx

I want to write that a quantity is of the order of say, 10 m/s. I have currently used the syntax below, but is there a way to write it completely into siunitx, or is the one considered below a reasonable way to do it?

$\mathcal{O}(\SI{10}{\meter\per\second})$


How about a mathtools-based solution? You get to decide whether to change \mathcal{O} to just the plain O without search/replace within your whole document. :)

\documentclass{article}
\usepackage{mathtools}
\usepackage{siunitx}
\setlength\parskip{\smallskipamount}

\DeclarePairedDelimiterXPP\BigOSI[2]%
{\mathcal{O}}{(}{)}{}%
{\SI{#1}{#2}}

\begin{document}

$\BigOSI{10}{\meter\per\second}$\par
$\BigOSI[\big]{10}{\meter\per\second}$

\end{document}


• Using it, I am not getting the bar symbol $Z=\BigOSI{}{\bar{r}(\bar{r}+\bar{\lambda})}$ – user1942348 Nov 17 at 9:08
• @user1942348, in your case you should not use suggested command adopted to specific use but just $Z=\mathcal{O} \bar{r}(\bar{r}+\bar{\lambda})$ – Zarko Nov 17 at 9:20