Adding Cross References

Last updated on 2025-07-03 | Edit this page

Overview

Questions

  • How can I ensure that numbers in my document are automatically updated?
  • How can I refer to numbered elements in my document?

Objectives

  • Insert a cross-reference in a LaTeX document.
  • Refer to a cross-referenced element in a LaTeX document.

Cross References

When writing a document of any length, you’ll often want to refer to numbered elements such as figures, tables, equations, or sections. LaTeX provides a way to automatically number these elements and refer to them in your text.

Label and Ref

To have LaTex remember a specific spot in your document, you have to use the \label{} command to mark it, and the \ref{} command to refer to it. For example:

LATEX 

\section{Cross References}
\label{sec:cross-references}

\subsection{Material for the Introduction}

In this section, we introduce two new concepts:

\begin{tabular}{cp{9cm}}
  \toprule
  Command & Description \\
  \midrule
  \kw{label} & Marks a spot in the document \\
  \kw{ref} & Refers to a marked spot in the document \\
  \bottomrule
\label{tab:cross-reference-commands}
\end{tabular}

We can \kw{refer} to the section with the \cmd{ref} command, like this: \ref{sec:cross-references}.
We can likewise refer to the table like this: \ref{tab:cross-reference-commands}.

Callout

The sec and tab prefixes in the \label{} command are not required, but they help to identify the type of element being labeled. This is especially useful when you have many labels in your document.

Caution

When you hit compile, you may notice that the \ref{} command does not return the correct references and instead shows question marks (??). This is because LaTeX needs to compile the document twice. Once to gather all the labels and references, and a second time to resolve them. If you see question marks, just compile the document again, and it should work correctly.

The label command always refers to the previous numbered entry: a section, a table, a figure, etc. This means that the \label{} command should always come after the numbered element you want to refer to.

Callout

Note that the ref command does not insert the section or table name, but rather the number associated with it. We would still write “Refer to Table \(\ref{tab:cross-reference-commands}\)”, but the benefit is that if the table number changes because we’ve added or removed sections before it, the reference will update automatically.

There are packages that can provide more advanced cross-referencing capabilities, such as the cleveref package, which can automatically detect the type of element being referenced and insert the appropriate name. For more details about this, refer to the references section.

Callout

If you want the references to be clickable in the PDF, you can use the hyperref package:

LATEX 

\usepackage{hyperref}

This package automatically makes all references clickable, allowing you to jump to the referenced element in the PDF document. However be aware that this can sometimes cause issues with other packages, so it’s best to load it last in your preamble.

Challenges

Challenge 1: Add a figure, then reference it.

In your LaTeX document, include the image example-image.PNG and cross-reference it in the text. Make sure the figure has a caption and is labeled and centered properly. Use the \includegraphics command to add the image and wrap it in a figure environment. Then, refer to it in the text using the \ref command.

You may find the following LaTeX template helpful.

LATEX 

\documentclass{article}
\usepackage{graphicx}

\begin{document}

\section{Cross-referencing Figures}



\end{document}

As shown in \(\ref{tab:findings}\) post-treatment values are higher…

LATEX 

\documentclass{article}
\usepackage{graphicx}


\begin{document}

\section{Cross-referencing Figures}

Here is an example of a figure in the document. We will refer to it later in the text.

\begin{figure}[ht]
  \centering
  \includegraphics[height=4cm]{example-image.PNG}
  \caption{This is an example figure.}
  \label{fig:example-image}
\end{figure}

In the text, we can refer to the figure using its label: Figure \ref{fig:example-image}.

\end{document}

Challenge 2: Where does the reference go?

We mentioned that the \label{} command should always come after the numbered element you want to refer to. What do you think would happen if we put the \label{} command before the numbered element? For example:

LATEX 

\documentclass{article}

\usepackage{lipsum}

\begin{document}

\section{Introduction}
\label{sec:intro}
\lipsum[1]

\label{sec:methods}
\section{Methodology}
\lipsum[2]

\section{Findings}
As indicated in Section \ref{sec:methods}, \lipsum[3][2]

\end{document}

The \lipsum package is a nice way of quickly generating large amounts of placeholder text - great if you just want to get an idea of how your document will look!

Before you run the code, think about what will happen. What do you expect the output to be? Run the code and see if your expectations were correct. Why or why not?

You might have expected the output to be either “As indicated in Section 2, …” or “As indicated in Section ???”, but it actually returns “As indicated in Section 1, …”. This is because the \label{} command marks the section number immediately preceding it. In this case, the \label{} command is placed before the \section{Methodology} command, so it marks the section number of the previous section, which is the Introduction section. The fact that the Introduction section already has a label does not matter.

Challenge 3: What’s wrong with this code?

Here’s a section from a larger document. Why might the references not be working as expected? (This is a tiny but common issue!)

LATEX 

\section{Findings}
\label{sec:findings}

\begin{table}[ht]
  \centering
  \begin{tabular}{lll}
    \toprule
    Color & Pre-treatment & Post-treatment \\
    \midrule
    Blue  & 30\% & 35\% \\
    Green & 15\% & 55\% \\
    Red   & 10\% & 12\% \\
    \bottomrule
  \end{tabular}
  \caption{Findings from the survey.}
  \label{tab:findings}
\end{table}

As shown in \ref{tab:findings} post-treatment values are higher...

The document compiles without error, but the reference text has an issue. What is it? Why does this happen?

The \ref{} command is correctly written, but the \ref{} command only returns the number of the label it is referring to. In this case, it will return the number of the table, not the name of the table. To fix this, you can write “As shown in Table \(\ref{tab:findings}\)…”

Key Points

  • The \label{} command marks a spot in the document.
  • The \ref{} command refers to a marked spot in the document.