How to change font size in LaTex equations

Credit should go to original contributor. I am just sharing here.

\documentclass{article} \usepackage{amsmath}
 \begin{document}

 \begin{eqnarray} 2x+3 \end{eqnarray}

 \makeatletter
 \def\@eqnnum{{\normalsize \normalcolor (\theequation)}}
  \makeatother
 { \small \begin{eqnarray} 2x+3 \end{eqnarray} }
 \end{document} 



to make sure the size of the equation numbers are not changed we have included a redefinition of the eqnnum command.
\makeatletter  \def\@eqnnum{{\normalsize \normalcolor (\theequation)}}  
\makeatother

available sizes:

• \tiny
• \scriptsize
• \footnotesize
• \small
• \normalsize (default)
• \large
• \Large (capital "L")
• \LARGE (all caps)
• \huge
• \Huge (capital "H")