Partager verticalement une feuille complète

\documentclass[a4paper]{article}
\usepackage{tikz}
\usetikzlibrary{calc}

\pagestyle{empty}

\begin{document}

\begin{tikzpicture}[remember picture, overlay]
\draw[shift={(current page.south west)}]
  let \p{page}=($(current page.north east) - (current page.south west)$),
      \n1 = { 1/9*\x{page} },
      \n2 = { 1/3*\y{page} } in
  (current page.south west) grid[xstep=\n1, ystep=\n2] (current page.north east);
\end{tikzpicture}

\end{document}