Left Align longtable Caption Beginning at Starting Point of Table

Question

I am having trouble left aligning longtable captions in Table 1, starting at the same table object left margin. I am essentially attempting to achieve what I have done in Table 2.

I came across a thread that recommends using LTcapwidth. This works when I manually alter textwidth factors (e.g. \setlength{\LTcapwidth}{.76\textwidth} for Table 1 in MWE), however, I am working on manuscript with a lot of longtables and would want to use a more flexible solution, rather than manually tweak \textwidth for all of them.

Minimum Working Example

\documentclass{article}

\usepackage{multirow}
\usepackage{longtable}
\usepackage{array}
\usepackage{booktabs}
\usepackage{floatrow}

\begin{document}

\section{Table Woes}

%%%\setlength{\LTcapwidth}{.76\textwidth}
\begin{longtable}[c]{
  @{} 
  >{\arraybackslash}p{0.10\linewidth}
  >{\arraybackslash}p{0.10\linewidth}
  >{\arraybackslash}p{0.10\linewidth}
  >{\arraybackslash}p{0.10\linewidth}
  >{\arraybackslash}p{0.10\linewidth}
  >{\arraybackslash}p{0.10\linewidth}
  @{}
}
  \caption{Caption needs to be left aligned beginning at same starting position as table}
  \label{tab:longtable_captionlable} \\
  \toprule
  Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\ 
  \midrule
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  \bottomrule
\end{longtable}


\begin{table}[h]
  \begin{floatrow}
  \ttabbox
  {\caption{Using floatrow, caption is properly left aligned from the beginning of left table margin.}\label{tab:table_captionlable}}
  {\begin{tabular}{|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|}
  \hline
  Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\ 
  \hline
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  \hline
  \end{tabular}}%
  \end{floatrow}
\end{table}
\end{document}

Answer 1

Since you're using floatrow, you can use a facility this package provides. From the docs:

7.2 The longtable Package

7.2.1 Additions in The floatrow Package

(...) If you'll write LTcapwidth=table or LTcapwidth=contents, you will get the caption width equal to the width of table.

You can set this key for longtables with \floatsetup[longtable]. Code:

\documentclass{article}

\usepackage{longtable}
\usepackage{array}
\usepackage{booktabs}
\usepackage{floatrow}

\floatsetup[longtable]{LTcapwidth=table}

\begin{document}

\section{Table Works}

\begin{longtable}[c]{@{}*{6}{>{\arraybackslash}p{0.10\linewidth}}@{}}
  \caption{Caption needs to be left aligned beginning at same starting
  position as table\label{tab:longtable_captionlable}}\\
  \toprule
  Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\ 
  \midrule
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  1 & 2 & 3 & 4 & 5 & 6 \\ 
  \bottomrule
\end{longtable}

\begin{table}[h]
  \ttabbox{%
    \caption{Using floatrow, caption is properly left aligned from the
      beginning of left table margin.}\label{tab:table_captionlable}%
  }{%
    \begin{tabular}{*{6}{|p{0.10\textwidth}}|}
      \hline
      Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\
      \hline
      1 & 2 & 3 & 4 & 5 & 6 \\
      1 & 2 & 3 & 4 & 5 & 6 \\
      1 & 2 & 3 & 4 & 5 & 6 \\
      \hline
    \end{tabular}%
  }%
\end{table}
\end{document}

Also note that you can use *{num}{cols}-expression in tabular column specification to improve code legibility.

Answer 2

Here is a simple solution:

\documentclass{article}

\usepackage{multirow}
\usepackage{longtable}
\usepackage{array}
\usepackage{booktabs}
\usepackage{floatrow}
\begin{document}

\section{Table Woes}


{\setlength{\LTcapwidth}{\dimexpr0.6\textwidth + 10\tabcolsep\relax}
\begin{longtable}{@{}*{6}{>{\arraybackslash}p{0.10\linewidth}}@{}}
 \caption{Caption needs to be left aligned beginning at same starting position as table}
 \label{tab:longtable_captionlable}\\
\endhead
  \toprule
  Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\
  \midrule
  1 & 2 & 3 & 4 & 5 & 6 \\
  1 & 2 & 3 & 4 & 5 & 6 \\
  1 & 2 & 3 & 4 & 5 & 6 \\
  \bottomrule
\end{longtable}}


\begin{table}[h]
  \begin{floatrow}
  \ttabbox
  {\caption{Using floatrow, caption is properly left aligned from the beginning of left table margin.}\label{tab:table_captionlable}}
  {\begin{tabular}{|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|p{0.10\textwidth}|}
  \hline
  Col 1 & Col 2 & Col 3 & Col 4 & Col 5 & Col 6 \\
  \hline
  1 & 2 & 3 & 4 & 5 & 6 \\
  1 & 2 & 3 & 4 & 5 & 6 \\
  1 & 2 & 3 & 4 & 5 & 6 \\
  \hline
  \end{tabular}}%
  \end{floatrow}
\end{table}

\end{document}