How to make the title of a table fit the width of the table

Question

I have the following table with title which is wider than the width of the tabular material. How do I make the title fit the the width of the table?

\documentclass{article}
\usepackage{caption,booktabs,array}
\usepackage[flushleft]{threeparttable}
\newcommand{\rowgroup}[1]{\hspace{-1em}#1}
\usepackage{geometry}
\geometry{
    a4paper,
    total={170mm,257mm},
    left=20mm,
    top=20mm,
}

\usepackage[width=.75\textwidth]{caption}
\begin{document}
\pagenumbering{gobble}
\begin{table}
\caption{Quite a long title for the table that tends to be wider than the table}
\centering
\begin{threeparttable}
\begin{tabular}{>{\quad}ll}
% \toprule
%& \multicolumn{1}{c}{} \\
\midrule
\rowgroup{Tests} \\
test1 &0.2\\
test2&0.2\\
test3&3.03\\
test3&0.006\\
\bottomrule
\end{tabular}
\end{threeparttable}
\end{table}
\end{document}

Answer 1

You're not using the threeparttable environment correctly: You should place the \caption statement inside rather than outside the threeparttable environment. That way, the caption's width will be restricted automatically to that of the tabular environment.

More generally, the three formal parts of a threeparttable environment are the \caption directive, the tabular environment (also possible: tabular* and tabularx), and the tablenotes environment. By placing the caption and the tablenotes material inside rather than outside the threeparttable environment, their widths will be adjusted automatically not to exceed the width of the tabular material.

\documentclass{article}
\usepackage{caption,booktabs,array,ragged2e}
\usepackage[flushleft]{threeparttable}
\newcommand{\rowgroup}[1]{\hspace{-1em}#1}
\usepackage{geometry}
\geometry{a4paper,total={170mm,257mm},left=20mm,top=20mm}

\usepackage[width=.75\textwidth]{caption}
\begin{document}
\begin{table}
%\captionsetup{justification=RaggedRight} % optional
\centering
\begin{threeparttable} % note that this comes before "\caption"
\caption{Quite a long title that's no longer wider than the subsequent tabular environment}
\begin{tabular}{>{\quad}ll}
\midrule
\rowgroup{Tests} \\
test1 &0.2\\
test2&0.2\\
test3&3.03\\
test3&0.006\\
\bottomrule
\end{tabular}
\end{threeparttable}
\end{table}
\end{document}

Answer 2

A simple solution is just add minipage into your tags, e.g.,

\documentclass{article}
\usepackage{caption,booktabs,array}
\usepackage[flushleft]{threeparttable}
\newcommand{\rowgroup}[1]{\hspace{-1em}#1}
\usepackage{geometry}
\geometry{
    a4paper,
    total={170mm,257mm},
    left=20mm,
    top=20mm,
}


\begin{document}
\pagenumbering{gobble}
\begin{table}
\begin{minipage}{80pt}
    \caption{Quite a long title for the table that tends to be wider than the table}
\centering
\begin{threeparttable}
\begin{tabular}{>{\quad}ll}
% \toprule
%& \multicolumn{1}{c}{} \\
\midrule
\rowgroup{Tests} \\
test1 &0.2\\
test2&0.2\\
test3&3.03\\
test3&0.006\\
\bottomrule
\end{tabular}
\end{threeparttable}
\end{minipage}
\end{table}
\end{document}

May be some experts will gives the auto fit option for this...

Answer 3

You can add backslash \\ in the caption:

\documentclass{article}
    \usepackage{caption,booktabs,array}
    \usepackage[flushleft]{threeparttable}

\newcommand{\rowgroup}[1]{\hspace{-1em}#1}

\usepackage{geometry}

\geometry{
        a4paper,
        total={170mm,257mm},
        left=20mm,
        top=20mm,
    }

\usepackage[width=.75\textwidth]{caption}

\begin{document}

\pagenumbering{gobble}

\begin{table}
        \caption{Quite a long title \\ for the table that tends \\ to be wider than
 the table}
    \centering
    \begin{threeparttable}
    \begin{tabular}{>{\quad}ll}
    % \toprule
    %& \multicolumn{1}{c}{} \\
    \midrule
    \rowgroup{Tests} \\
    test1 &0.2\\
    test2&0.2\\
    test3&3.03\\
    test3&0.006\\
    \bottomrule
    \end{tabular}
    \end{threeparttable}
    \end{table}

\end{document}