\documentclass{article}

\usepackage{caption}
\DeclareCaptionFont{14pt}{\fontsize{14pt}{12pt}\selectfont}
\captionsetup{font=14pt}

\begin{document}

Some regular text set in \verb|\normalsize|.
\begin{table}[t]
  \caption{A table using \texttt{14pt}.}
\end{table}
\begin{figure}[t]
  \caption{A figure using \texttt{14pt}.}
\end{figure}

\end{document}