LaTeX Lengths and Units

Complete guide to LaTeX measurement units, lengths, and spacing. Learn how to use points, ems, centimeters, and other units for precise document formatting.

Understanding LaTeX lengths and units is essential for precise document formatting. This guide covers all measurement units, how to use them effectively, and practical examples for common formatting tasks.

Key concept: LaTeX uses different units for different purposes. Understanding when to use each unit type will help you create professional, consistent documents.

Related topics: Page layout | Spacing | Document design

LaTeX Units Overview

Absolute Units

Fixed measurements that don’t change based on font or context.

Unit	Name	Equivalent	Best Used For
pt	Point	1 pt = 1/72.27 inch	Font sizes, line widths
pc	Pica	1 pc = 12 pt	Typography measurements
in	Inch	1 in = 72.27 pt	Page dimensions
cm	Centimeter	1 cm = 28.45 pt	Metric page layout
mm	Millimeter	1 mm = 2.845 pt	Precise measurements
bp	Big point	1 bp = 1/72 inch	PostScript compatibility
dd	Didot point	1 dd = 1.07 pt	European typography
cc	Cicero	1 cc = 12 dd	European typography
sp	Scaled point	1 sp = 1/65536 pt	Internal calculations

Relative Units

Units that scale with font size or document context.

Unit	Name	Relative To	Best Used For
em	Em	Current font size	Font-dependent spacing
ex	Ex	Height of letter ‘x’	Vertical spacing
en	En	Half the width of ‘M’	Horizontal spacing
mu	Math unit	1/18 em in math mode	Math spacing

Basic Length Usage

Setting Lengths

basic-lengths.tex

\documentclass{article}
\usepackage[margin=1in]{geometry}

\begin{document}

% Setting margins
\newgeometry{left=2cm, right=2cm, top=3cm, bottom=3cm}

% Horizontal spacing
This text\hspace{2cm}has 2cm space.

% Vertical spacing
This is the first line.
\vspace{1in}
This line is 1 inch below.

% Paragraph indentation
\setlength{\parindent}{0.5in}
This paragraph is indented by half an inch.

% Line spacing
\setlength{\baselineskip}{14pt}
This text has 14pt baseline skip.

\end{document}

Measuring Existing Elements

measuring.tex

\documentclass{article}
\begin{document}

% Get current values
The current font size is \the\fontdimen6\font pt.

% Text width measurements
Text width: \the\textwidth

Line height: \the\baselineskip

Paragraph indent: \the\parindent

% Using lengths in calculations
\newlength{\mywidth}
\setlength{\mywidth}{0.5\textwidth}
This box is half text width: \fbox{\parbox{\mywidth}{Content here}}

\end{document}

Practical Applications

Page Layout Dimensions

page-dimensions.tex

\documentclass{article}
\usepackage{geometry}

% Absolute measurements
\geometry{
    paperwidth=210mm,      % A4 width
    paperheight=297mm,     % A4 height
    left=25mm,             % Left margin
    right=25mm,            % Right margin
    top=30mm,              % Top margin
    bottom=30mm            % Bottom margin
}

% Relative to paper size
\geometry{
    width=0.8\paperwidth,  % 80% of paper width
    height=0.9\paperheight % 90% of paper height
}

\begin{document}

Current page dimensions:
\begin{itemize}
\item Paper width: \the\paperwidth
\item Paper height: \the\paperheight
\item Text width: \the\textwidth
\item Text height: \the\textheight
\end{itemize}

\end{document}

Font-Relative Spacing

font-relative.tex

\documentclass{article}
\begin{document}

% Em-based spacing (scales with font size)
{\normalsize Normal text with \hspace{2em} 2em space.}

{\large Large text with \hspace{2em} 2em space.}

{\huge Huge text with \hspace{2em} 2em space.}

% Ex-based spacing (scales with x-height)
Baseline text\vspace{2ex}
Text with 2ex vertical space above.

% Comparison of units
\begin{tabular}{ll}
2cm space: & Text\hspace{2cm}continues \\
2em space: & Text\hspace{2em}continues \\
2ex space: & Text\hspace{2ex}continues \\
\end{tabular}

\end{document}

Advanced Length Operations

Length Arithmetic

length-arithmetic.tex

\documentclass{article}
\usepackage{calc}

\begin{document}

% Define custom lengths
\newlength{\sidebarwidth}
\newlength{\mainwidth}

% Calculate widths
\setlength{\sidebarwidth}{0.25\textwidth}
\setlength{\mainwidth}{\textwidth - \sidebarwidth - 1cm}

% Use in layout
\noindent
\begin{minipage}{\sidebarwidth}
\textbf{Sidebar}\\
Content here
\end{minipage}%
\hspace{1cm}%
\begin{minipage}{\mainwidth}
\textbf{Main Content}\\
This is the main content area calculated to fit properly.
\end{minipage}

% Complex calculations
\newlength{\complexwidth}
\setlength{\complexwidth}{(\textwidth - 3\columnsep) / 2}

Width calculation: \the\complexwidth

\end{document}

Conditional Lengths

conditional-lengths.tex

\documentclass{article}
\usepackage{ifthen}

\begin{document}

% Set length based on conditions
\newlength{\dynamicspace}

\ifthenelse{\lengthtest{\textwidth > 400pt}}
  {\setlength{\dynamicspace}{2cm}}
  {\setlength{\dynamicspace}{1cm}}

Dynamic spacing: \the\dynamicspace

% Responsive margins
\newcommand{\responsivemargin}{%
  \ifthenelse{\lengthtest{\textwidth > 500pt}}
    {2cm}
    {1cm}
}

\newgeometry{margin=\responsivemargin}

\end{document}

Spacing Commands

Horizontal Spacing

horizontal-spacing.tex

\documentclass{article}
\begin{document}

% Fixed horizontal spaces
Word\hspace{1cm}space

% Flexible spaces
Left\hfill Right

% Negative space
Over\hspace{-2mm}lap

% Stretchable space
\hspace{1cm plus 1cm minus 0.5cm}

% Fill remaining space
Text\hfill\hfill More text

% Specific spacing commands
Thin\,space (3/18 em)
Medium\:space (4/18 em)
Thick\;space (5/18 em)
Quad\quad space (1 em)
Double\qquad space (2 em)

\end{document}

Vertical Spacing

vertical-spacing.tex

\documentclass{article}
\begin{document}

First paragraph.

\vspace{2cm}
Paragraph with 2cm space above.

\vspace*{1in}
Paragraph with 1 inch space that won't disappear at page breaks.

% Stretchable vertical space
\vspace{1cm plus 2cm minus 0.5cm}
Flexible space above this paragraph.

% Fill remaining page
Content at top.
\vfill
Content at bottom.

% Negative vertical space
Line one.
\vspace{-\baselineskip}
Line that overlaps above.

\end{document}

Length Variables and Customization

Document-Wide Settings

document-settings.tex

\documentclass{article}

% Customize default lengths
\setlength{\parindent}{2em}        % Paragraph indentation
\setlength{\parskip}{1ex plus 0.5ex} % Space between paragraphs
\setlength{\baselineskip}{14pt}    % Line spacing
\setlength{\columnsep}{2em}        % Column separation

% Custom length variables
\newlength{\sectionspace}
\setlength{\sectionspace}{2ex plus 1ex minus 0.5ex}

\newlength{\figuremargin}
\setlength{\figuremargin}{1cm}

\begin{document}

% Use custom lengths
\section{Introduction}
\vspace{\sectionspace}

Normal paragraph with custom settings.

% Dynamic adjustments
\addtolength{\leftskip}{2em}
This paragraph is indented by 2em on the left.
\addtolength{\leftskip}{-2em}

Back to normal margins.

\end{document}

Creating Length Commands

length-commands.tex

\documentclass{article}

% Custom spacing commands
\newcommand{\smallgap}{\vspace{0.5\baselineskip}}
\newcommand{\mediumgap}{\vspace{\baselineskip}}
\newcommand{\largegap}{\vspace{2\baselineskip}}

% Responsive spacing
\newcommand{\smartspace}[1]{%
  \ifthenelse{\lengthtest{#1 > 2cm}}
    {\vspace{#1}}
    {\vspace{2cm}}%
}

% Context-aware spacing
\newcommand{\sectiongap}{%
  \ifthenelse{\equal{\@currsize}{\large}}
    {\vspace{1.5ex}}
    {\vspace{1ex}}%
}

\begin{document}

First section.
\smallgap

Second section.
\mediumgap

Third section.
\largegap

Fourth section with large gap.

\end{document}

Math Mode Spacing

Math Units

math-spacing.tex

\documentclass{article}
\usepackage{amsmath}

\begin{document}

% Math mode spacing units
\begin{align}
f(x) &= x^2 \quad \text{(1 em space)} \\
g(x) &= x^3 \qquad \text{(2 em space)} \\
h(x) &= x^4 \, \text{(thin space)} \\
i(x) &= x^5 \: \text{(medium space)} \\
j(x) &= x^6 \; \text{(thick space)} \\
k(x) &= x^7 \! \text{(negative thin space)}
\end{align}

% Custom math spacing
\begin{equation}
\int_0^\infty \! f(x) \, dx = \sum_{n=0}^\infty \, a_n
\end{equation}

% Math spacing commands
\[
\text{Thin: } a\,b \quad
\text{Medium: } a\:b \quad  
\text{Thick: } a\;b \quad
\text{Quad: } a\quad b
\]

\end{document}

Units in Different Contexts

Tables and Figures

table-figure-units.tex

\documentclass{article}
\usepackage{graphicx}
\usepackage{booktabs}

\begin{document}

% Table with unit-based sizing
\begin{table}[h]
\centering
\begin{tabular}{p{3cm}p{4cm}p{2cm}}
\toprule
Fixed 3cm & Fixed 4cm & Fixed 2cm \\
\midrule
Content adapts & to specified & column width \\
\bottomrule
\end{tabular}
\caption{Table with fixed column widths}
\end{table}

% Figure scaling with units
\begin{figure}[h]
\centering
% Scale by absolute size
\includegraphics[width=8cm]{example-image}
\caption{Figure scaled to 8cm width}
\end{figure}

% Relative scaling
\begin{figure}[h]
\centering
\includegraphics[width=0.8\textwidth]{example-image}
\caption{Figure scaled to 80\% of text width}
\end{figure}

\end{document}

Custom Environments

custom-environments.tex

\documentclass{article}
\usepackage{framed}

% Define environment with custom spacing
\newenvironment{myquote}[1][2em]
{%
  \vspace{1ex}%
  \begin{quote}%
  \leftskip=#1%
  \rightskip=#1%
  \itshape%
}
{%
  \end{quote}%
  \vspace{1ex}%
}

\begin{document}

Regular paragraph text.

\begin{myquote}
This is a quote with default 2em indentation.
\end{myquote}

\begin{myquote}[4em]
This quote has 4em indentation on both sides.
\end{myquote}

Regular text continues.

\end{document}

Best Practices

Unit selection guidelines:

1. Use em for font-dependent spacing - Scales automatically with font changes
2. Use ex for vertical spacing - Based on lowercase letter height
3. Use pt for precise control - When exact measurements are needed
4. Use cm/mm for page layout - Intuitive for physical dimensions
5. Use relative units when possible - Better for responsive designs
6. Avoid mixing unit systems - Stick to metric OR imperial consistently

Common Patterns

best-practices.tex

\documentclass{article}

% Good: Font-relative spacing
\setlength{\parskip}{0.5\baselineskip plus 0.2\baselineskip}

% Good: Consistent unit system
\geometry{margin=2.5cm, marginparwidth=2cm}

% Good: Flexible spacing
\newcommand{\flexspace}{\vspace{1ex plus 0.5ex minus 0.2ex}}

% Avoid: Mixing systems inconsistently
% \geometry{margin=1in, marginparwidth=3cm}  % Don't mix

% Good: Relative to context
\newlength{\myindent}
\setlength{\myindent}{2em}  % Scales with font

\begin{document}

Properly spaced content with consistent units.

\end{document}

Debugging Length Issues

Measuring and Displaying

debugging-lengths.tex

\documentclass{article}
\usepackage{layouts}

\begin{document}

% Display current settings
\begin{itemize}
\item Text width: \the\textwidth
\item Text height: \the\textheight
\item Line height: \the\baselineskip
\item Paragraph indent: \the\parindent
\item Paragraph skip: \the\parskip
\end{itemize}

% Show page layout
\currentpage
\pagediagram

% Measure specific elements
\newlength{\testlength}
\settowidth{\testlength}{Sample text to measure}
Width of "Sample text to measure": \the\testlength

\settoheight{\testlength}{Sample text}
Height of "Sample text": \the\testlength

\end{document}

Quick Reference

Essential Length Commands

Command	Purpose	Example
\hspace{length}	Horizontal space	\hspace{2cm}
\vspace{length}	Vertical space	\vspace{1ex}
\setlength{\variable}{length}	Set length variable	\setlength{\parindent}{2em}
\addtolength{\variable}{length}	Modify length	\addtolength{\textwidth}{-2cm}
\newlength{\variable}	Create length variable	\newlength{\mywidth}

Common Length Variables

Variable	Description
\textwidth	Width of text area
\textheight	Height of text area
\paperwidth	Paper width
\paperheight	Paper height
\baselineskip	Line spacing
\parindent	Paragraph indentation
\parskip	Space between paragraphs

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Next: Learn about Headers and footers to customize page headers and footers, or explore Page numbering for advanced numbering schemes.