LaTeX Forum

\documentclass{article}
\usepackage{siunitx}

\begin{document}

\sisetup{detect-weight, detect-inline-weight = math, detect-display-math=true}
\mathversion{bold}
$x = \SI{5}{\watt}$

\begin{equation}
x = \SI{5}{\watt}
\end{equation}

\end{document}

\documentclass{article}
\usepackage{siunitx}
\sisetup{detect-all}
\begin{document}
\bfseries
\begin{equation}
		\mathbf{\Sigma\dot{Q}_{W,R}=}\SI{721,33}{\watt}
\end{equation} 
\end{document}

% 
\begin{equation*}
\begin{aligned}
\mathbf{\Sigma\dot{Q}_{W,R}}=\mathbf{\SI{721,33}{\watt}}
\end{aligned}
\end{equation*}