How do I reduce the size of an entire LaTeX table?

Use \resizebox:

\resizebox{3cm}{!}{
  \begin{something}
    something
  \end{something}
  }

The ! tells LaTeX to keep the aspect ratio. You can also scale the y direction differently by giving a value there.

Scaling elements that contain text is really not a good idea (see https://tex.stackexchange.com/questions/425453/why-not-scale-elements-that-contain-text for more information) therefore here are two other approaches how to reduce the size of a table:

• reducing the inter column space with \addtolength{\tabcolsep}{-1pt}
• manually selecting a smaller font size, e.g. with font commands like \small or for more fine control \fontsize{9.5pt}{10.25pt}\selectfont

---

\documentclass{article}

\usepackage{lipsum}

\begin{document}

Reducing the inter column spacing a bit:
\begin{table}[htbp]
\addtolength{\tabcolsep}{-1pt}
\begin{tabular}{lll}
\hline
some text some text & some text some text & some text some text some text\\
\hline
\end{tabular}
\end{table}

\lipsum[2]

Smaller font size:
\begin{table}[htbp]
\small
\begin{tabular}{lll}
\hline
some text some som text & some text some text & some text some text some text\\
\hline
\end{tabular}
\end{table}


\end{document}