% !TEX TS-program = xelatex
% !TEX encoding = UTF-8 Unicode

\documentclass[11pt]{article}

\usepackage{calc}
\usepackage{tikz}
\usetikzlibrary{calc,positioning,backgrounds,matrix}

\newlength\margin{}
\setlength\margin{1cm}

\usepackage[margin=\margin, noheadfoot, a4paper]{geometry}

\newlength\sidewidth{}
\setlength\sidewidth{0.3\paperwidth-\margin}

\newlength\mainwidth{}
\setlength\mainwidth{\paperwidth-4\margin-\sidewidth}

\begin{document}
Sample text
\end{document}