Typesetting Units in LaTeX
Use this macro to tell 
that you don’t want your units slanted in math mode.
\newcommand{\unit}[1]{\ensuremath{\, \mathrm{#1}}}Example
$ m = 5 kg $will render as “m = 5 kg”.$ m = 5 \unit{kg} $will render as “m = 5 kg”.
“I want more!”
Use the units.sty package if my macro is not enough for you.