\documentclass[a4paper, 12pt]{article}
\pagestyle{empty}

\usepackage{polski}
\usepackage[cp1250]{inputenc}

\begin{document}

3 punkty drukarskie: \rule{3pt}{12pt}

\medskip

3 milimetry: \rule{3mm}{12pt}

\medskip

3 centymetry: \rule{3cm}{12pt}

\medskip

3 cale: \rule{3in}{12pt}

\medskip

1 x wysokość litery x: \rule{1cm}{1ex}

\medskip

\newsavebox{\mybox}
\sbox{\mybox}{x}
\the\ht\mybox

\sbox{\mybox}{\rule{1cm}{1ex}}
\the\ht\mybox

\medskip

$\approx$ 1 x rozmiar czcionki: \rule{1cm}{1em}

\medskip

\sbox{\mybox}{M}
\the\wd\mybox

\sbox{\mybox}{\rule{1cm}{1em}}
\the\ht\mybox

\bigskip\bigskip

\verb+\rule[przesunięcie]{szerokość}{wysokość}+

\bigskip

\rule{3mm}{.1pt}%
\rule[-2mm]{5mm}{1cm}%
\rule{3mm}{.1pt}%
\rule[2mm]{1cm}{5mm}%
\rule{3mm}{.1pt}%

\bigskip

\begin{center}
\rule[1ex]{\textwidth}{2pt}
{\sc Śliczny tekst pomiędzy krechami}
\rule{\textwidth}{2pt}
\end{center}


\end{document}
