multicolumn tabularx extending page width

Question

I have used multicolumn and tabularx for the table I intend to write in LaTex. But the resultant table is going out of the page width. I also added the textwidth in tabularx but it is not working as desired. Surely, I have did some mistake but cant figure out. Would be glad to have the correction. Thank you

\begin{table}
\centering
\caption{my table}
\label{mytable}
\begin{tabularx}{\textwidth}{|c|c|c|c|X|c|X|} 
\hline
\multicolumn{1}{|l|}{Type} & \multicolumn{1}{l|}{Product name} & \multicolumn{1}{l|}{\begin{tabular}[c]{@{}l@{}}Diameter\\(mm)\end{tabular}} & \multicolumn{1}{l|}{\begin{tabular}[c]{@{}l@{}}Tensile strength\\(MPa)\end{tabular}} & \multicolumn{1}{l|}{\begin{tabular}[c]{@{}l@{}}Young's modulus\\(GPa)\end{tabular}} & \multicolumn{1}{l|}{\begin{tabular}[c]{@{}l@{}}Elongation\\(\%)\end{tabular}} & Application \\ 
\hline
\multirow{5}{*}{\begin{tabular}[c]{@{}c@{}}class A\\~\\~\\~\\ \end{tabular}} & abc123 & 0.014 & 1500 & 36 & 7 & four words text here  \\ 
\cline{2-7} & abc123 & 0.040 & 1400 & 36 & 6.5 & four words text here\\ 
\cline{2-7} & abc123 & 0.20 & 975 & 27 & 9 & four words text here \\ 
\cline{2-7} & abc123 & 0.31 & 975 & 26 & 6 & four words text here \\ 
\cline{2-7} & abc123 & 0.67 & 900 & 23 & 9 & four words text here \\ \hline
\multicolumn{1}{|l|}{\multirow{3}{*}{class B}} & abc123 & 0.027 & 1560 & 39 & 6.5 & four words text here  \\ 
\cline{2-7} \multicolumn{1}{|l|}{} & abc123 & 0.040 & 1600 & 41 & 6.5 & four words text here \\ 
\cline{2-7} \multicolumn{1}{|l|}{} & abc123 & 0.10 & 1200 & 28 & 12.5 & four words text here \\
\hline
\end{tabularx}
\end{table}

Also, the merged column text of the first column, I want it to set the vertical alignment to center instead of top.

Answer 1

The reason the tabularx environment's width exceeds the width of the textblock is that you're not allowing line breaks in the header cells. I suggest that you (a) radically simplify the header material, mostly by getting rid of the \multicolumn "wrappers", and (b) use a centered version of the X column type for all six data columns. Optionally, consider using a separate row in the header to place the information about the units of measurement.

\documentclass{article}
\usepackage{tabularx}  % for "tabularx" environment and "X" column type
\usepackage{ragged2e}  % for "\Centering" macro
\newcolumntype{C}{>{\Centering\arraybackslash\hspace{0pt}}X}
%% "\hspace{0pt}" allows for hyphenation of first word in header cells

\begin{document}

\begin{table}
%%\centering % not needed
\caption{My table}
\label{tab:mytable}
\setlength\extrarowheight{2pt} % for a slightly more open "look"
\setlength\tabcolsep{3pt}      % default: 6pt

\begin{tabularx}{\textwidth}{|l|*{6}{C|}} 
\hline
Type & Product name & Diameter & Tensile strength 
     & Young's modulus & Elongation & Application \\ 
& & (mm) & (MPa) & (GPa) & (\%) & \\ % place units of measurement on a separate row
\hline
Class A  & abc123 & 0.014 & 1500 & 36 & 7   & four words text here \\ \cline{2-7} 
         & abc123 & 0.040 & 1400 & 36 & 6.5 & four words text here \\ \cline{2-7} 
         & abc123 & 0.20  &  975 & 27 & 9   & four words text here \\ \cline{2-7} 
         & abc123 & 0.31  &  975 & 26 & 6   & four words text here \\ \cline{2-7} 
         & abc123 & 0.67  &  900 & 23 & 9   & four words text here \\ 
\hline
Class B  & abc123 & 0.027 & 1560 & 39 & 6.5 & four words text here \\ \cline{2-7}  
         & abc123 & 0.040 & 1600 & 41 & 6.5 & four words text here \\ \cline{2-7}  
         & abc123 & 0.10  & 1200 & 28 & 12.5& four words text here \\
\hline
\end{tabularx}
\end{table}

\end{document}

---

Addendum: If this were my table, I'd strive to give it a far more open and "inviting" look. I'd do so mainly by (a) getting rid of all vertical rules and (b) using fewer, but well-spaced, horizontal rules. The booktabs package, and its macros \toprule, \midrule, and \bottomrule, are made for just this use case.

\documentclass{article}
\usepackage{tabularx,ragged2e,siunitx,booktabs}
\newcolumntype{C}{>{\Centering\arraybackslash\hspace{0pt}}X}

\begin{document}
\begin{table}
\caption{Second try}
\label{tab:secondtry}
\setlength\tabcolsep{4pt}      % default: 6pt

\begin{tabularx}{\textwidth}{@{} l *{6}{C} @{}} 
\toprule
Type & Product name & Diameter & Tensile strength 
     & Young's modulus & Elongation & Application \\ 
& & (\si{\milli\meter}) & (\si{\mega\pascal}) & (\si{\giga\pascal}) & (\%) & \\
\midrule
Class A  & abc123 & 0.014 & 1500 & 36 & 7   & four words text here \\ \addlinespace 
         & abc123 & 0.040 & 1400 & 36 & 6.5 & four words text here \\ \addlinespace 
         & abc123 & 0.20  &  975 & 27 & 9   & four words text here \\ \addlinespace 
         & abc123 & 0.31  &  975 & 26 & 6   & four words text here \\ \addlinespace 
         & abc123 & 0.67  &  900 & 23 & 9   & four words text here \\ 
\midrule
Class B  & abc123 & 0.027 & 1560 & 39 & 6.5 & four words text here \\ \addlinespace  
         & abc123 & 0.040 & 1600 & 41 & 6.5 & four words text here \\ \addlinespace  
         & abc123 & 0.10  & 1200 & 28 & 12.5& four words text here \\
\bottomrule
\end{tabularx}
\end{table}

\end{document}