## Class files

In L a T e X there are a lot of lengths determining various dimensions of prepared documents. For example, specified dimension parameters characterize fonts , pages , or paragraphs .

# Units

Below a description of available units in L a T e X .

Abbreviation Value
pt a point is approximately 1/72.27 inch, that means about 0.0138 inch or 0.3515 mm (exactly point is defined as 1/864 of American printerâs foot that is 249/250 of English foot)
mm a millimeter
cm a centimeter
in inch
ex roughly the height of an 'x' (lowercase) in the current font (it depends on the font used)
em roughly the width of an 'M' (uppercase) in the current font (it depends on the font used)
mu math unit equal to 1/18 em, where em is taken from the math symbols family

Below an example that shows the difference between ex and em units.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amssymb}
\usepackage{graphicx}

\begin{document}
Example of a picture with different lenghts
\includegraphics[width=15ex]{lion-logo}

\includegraphics[width=15em]{lion-logo}
\end{document}

# Lengths

Lengths are units of distance relative to some document elements. Lengths can be changed by the command:

\setlength{\lengthname}{value_in_specified_unit}

For example, in a two-column document the column separation can be set to 1 inch by:

\setlength{\columnsep}{1in}

Below is a table with some of the most common lengths and their description

Length Description
 \baselineskip  Vertical distance between lines in a paragraph
 \columnsep  Distance between columns
 \columnwidth  The width of a column
 \evensidemargin  Margin of even pages, commonly used in two-sided documents such as books
 \linewidth  Width of the line in the current environment.
 \oddsidemargin  Margin of odd pages, commonly used in two-sided documents such as books
 \paperwidth  Width of the page
 \paperheight  Height of the page
 \parindent  Paragraph indentation
 \parskip  Vertical space between paragraphs
 \tabcolsep  Separation between columns in a table (tabular environment)
 \textheight  Height of the text area in the page
 \textwidth  Width of the text area in the page
 \topmargin  Length of the top margin

# Using lengths as units

Default lengths can not only be set to any desired value, they can also be used as units to set the dimensions of other L a T e X elements. For instance, you can set an image to have a width of one quarter the total text width.

\includegraphics[width=0.25\textwidth]{lion-logo}
[...]

In the command  \includegraphics  the width is set to 0.25 the width of the entire text area (see Inserting Images for more information about this command). You can use any length and multiply it by any factor.