Typesetting image scale in SI units using the siunitx package

Question

I use the siunitx package to consistently typeset units in my thesis. One particular typesetting format I'm interested in is the format of scales.

Let's say I'm describing a 5-by-5µm image. I fiddled around with the commands and found that I can do the following \SI{5x5}{\micro\meter}. This command, however, displays the scale as 5 µm x 5 µm.

I'd like to change the behavior of the package to display the units only once, as in "5x5 µm", as it is more compact and avoids the repetition of the unit in the text.

Is there an option or alternate syntax command that I should use?

Answer 1

You want the product-units option

\documentclass{article}
\usepackage{siunitx}
\begin{document}
\SI[product-units = single]{5x5}{\um}
\end{document}

(Note: this is mathematically questionable as it's the product of an integer and a length, not the product of two lengths.)

Answer 2

You could also use the \si macro, instead of the \SI macro, to typeset just the unit part of the expression:

{5$\times$5}\,\si{\micro\meter}

However, I agree with Joseph Wright that this form of expressing a scale is mathematically questionable.