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Can anyone tell how to put the capital Angstrom to express units. I have been looking for a package but I haven't found one yet.

José Andrés Arcos
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    \AA is not OK? – Przemysław Scherwentke Feb 02 '18 at 04:12
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    \AA is invalid in math mode. In math mode, put it in \text{} as \(\text{\AA}\), or see some solutions at this question – ydhhat Jun 06 '21 at 18:39
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    @ydhhat If you use \text, the formatting of the surrounding text will bleed through to math mode. This most often happens with italics in theorem statements. You probably would want \textnormal to rest the formatting, or \textup if you want to clear italics/small caps but use bold math in a header. Or, use siunitx. – Davislor Aug 23 '21 at 14:48

3 Answers3

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The excellent siunitx package is there for you: 

\documentclass{article}

\usepackage{siunitx}

\begin{document}

\si{\angstrom}

\SI{1}{\angstrom}

\end{document}
user94293
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    Unfortunately, \angstrom has been deprecated in siunitx from version 2 to 3 (as it is not an official SI unit), it has to be defined as a custom unit, examples: https://tex.stackexchange.com/questions/24255/angstrom-not-working Also, \SI has been replaced by \qty{} commands. – escalator Jun 07 '21 at 06:59
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    \DeclareSIUnit{\angstrom}{\textup{\AA}} – user94293 Dec 30 '22 at 22:00
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Actually, simply typing

\r{A}

works fine! Also, it seems that it does not need any package, not even the ams packages, which is a bit strange).

P.S.: I do not have the unitx package installed (I want to install it, but for the moment to do not know how to install it on miktex..)

Wendigo
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An alternative that works in both text and math mode is

\textup{~\AA}

This always sets the unit upright, but makes it bold if you use it in a header. It also avoids line breaking between a quantity and its unit. In practice, you’d end up defining a macro for this that’s no simpler than \qty from siunitx.

Davislor
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