siunitx

Typeset physical quantities, SI units and well-formatted numbers with automatic digit grouping.

Example
Preamble

$Rendered LaTeX output$

Numbers can be written plain text (such as 100), by using the \href{https://ctan.org/pkg/siunitx}{siunitx} package as follows:
\SI{100}{\km\per\hour},
or by using plain \LaTeX{} (and math mode):
$100 \frac{\mathit{km}}{h}$.

$Rendered LaTeX output$

\SI{5}{\percent} of \SI{10}{kg}

$Rendered LaTeX output$

Numbers are automatically grouped: \num{123456}.

\usepackage[group-minimum-digits=4,per-mode=fraction]{siunitx}