calorie unit with siunitx

Question

How to get the calorie unit in siunitx package. Thanks

\documentclass{memoir}
\usepackage{siunitx}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
\si[per-mode=symbol]{\kilo**\cal**\per\mol}
\end{document}

Answer 1

Package chemmacros defines that unit for you along with some other useful stuff. Currently, using chemmacros with memoir will lead to a small warning.

\documentclass{memoir}
\usepackage{amsmath}
\usepackage{chemmacros}
\usepackage{amssymb}
\sisetup{per-mode=symbol}
\newcommand{\therm}{\text{th}}
\begin{document}
$\mathrm{cal}_\therm = \SI{1}{\kilo\cal\per\mol} =
\SI{4184}{\joule\per\mol}$ where \si{\mol} is a base SI unit related to
the Avogrado constant ($N_A = \num{6.02214129e23}$).

Water has a molar mass of $M(\ch{H2O})\approx \SI{18}{\MolMass}$
\end{document}

Because chemmacros is providing quite some features, the list of needed packages is quite long. If you just need that one unit, you can savely define it yourself.

\documentclass{memoir}
\usepackage{amsmath}
\usepackage{siunitx}
\usepackage{amssymb}
\DeclareSIUnit{\calorie}{cal}
\DeclareSIUnit{\Calorie}{\kilo\calorie}
\sisetup{per-mode=symbol}
\begin{document}
Dancing Ducks need to eat up to \SI{1000}{\Calorie} each day.
\end{document}

Answer 2

You can define your own units with siunitx:

\documentclass[a4paper]{article}

\usepackage{siunitx}
\DeclareSIUnit[number-unit-product = {\,}]
\cal{cal}
\DeclareSIUnit\kcal{\kilo\cal}
\DeclareSIUnit[number-unit-product = {\,}]
\Btu{Btu}
\DeclareSIUnit[number-unit-product = {\,}]
\Fahr{\degree F}
\DeclareSIUnit[number-unit-product = {\,}]
\lb{lb}

\begin{document}

 $ \SI{1}{\cal} = \SI{4.18400}{\J}$

 $ \SI{1}{\kcal} = \SI{4184}{\N\m}$

 $ 1 $ hamburger $ = \SI{1}{\mega\cal}$\\

A possible conversion of \emph{British Thermal Unit}, which is the energy needed to heat $ \SI{1}{\lb} $ of water from $ \SI{58.1}{\Fahr} $ to $ \SI{59.1}{\Fahr} $ :\smallskip

$ \SI{1}{\Btu} = \SI{1055,05585262}{\J} $

\end{document}