# columns have not the same size although centered

I made a table like this one

\documentclass{article}
\usepackage{array}
\usepackage{booktabs}
\begin{document}
\begin{table}[htb]
\centering
\caption{Reproduzierbarkeit der Elektroden}
\begin{tabular}{ccccc|c|c|c|c|}
\toprule
\textbf{Elektrode} &\multicolumn{4}{c}{\textbf{Mittelwert [mV]}} &\multicolumn{4}{c}{\textbf{maximale Abweichung [\%]}} \\
\midrule
&pH 6 &pH 7 & pH 8 &pH 9 &pH 6 &pH 7 &pH 8&pH 9\\
\cmidrule[0.5pt]{2-9}
6 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
7 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
8 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
9 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
\bottomrule
\label{tab:reproduzierbarkeit}
\end{tabular}
\end{table}
\end{document}


and what I get is:

So why is the width of the ninth column bigger than the others, although all rows are centered? How can I change this, so that each column has the same width?

Thanks!

-
Do you mean the width of the last column? It's because of the \multicolumn above I'd think, it is wider than the four columns below, so additional width is added to the last column. (Edit: rows are horizontal, columns are vertical.) –  Torbjørn T. Mar 16 '14 at 19:21
Oh sorry, I changed it. Yes I mean the width. How can I fix it, that they are equal? –  user47091 Mar 16 '14 at 19:33
It is basically the same problem as tex.stackexchange.com/questions/128736/… I think, you could try using Mico's suggestion. –  Torbjørn T. Mar 16 '14 at 19:48
@TorbjørnT. I think you can do it without tabularx and without needing to know the overall width of the tabular. Does my deleted-edited-undeleted answer do what's wanted here? (I'm not sure if it is quite right...) –  cfr Mar 16 '14 at 19:59

You need to make sure that the spanned cells are wider than the multicolumn entry.

\documentclass{article}
\usepackage{array}
\usepackage{booktabs}
\begin{document}
\begin{table}[htb]
\centering
\newcommand\x{\makebox[1pt]{}}
\caption{Reproduzierbarkeit der Elektroden}
\begin{tabular}{@{}c*4{>\x c<\x}|*4{>\x c<\x|}@{}}
\toprule
\textbf{Elektrode} &\multicolumn{4}{c}{\textbf{Mittelwert [mV]}} &\multicolumn{4}{c}{\textbf{maximale Abweichung [\%]}} \\
\midrule
&pH 6 &pH 7 & pH 8 &pH 9 &pH 6 &pH 7 &pH 8&pH 9\\
\cmidrule[0.5pt]{2-9}
6 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
7 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
8 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
9 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
\bottomrule
\label{tab:reproduzierbarkeit}
\end{tabular}
\end{table}
\end{document}

-
@TorbjørnT. thanks, fixed and image updated:-) –  David Carlisle Mar 16 '14 at 20:45

You could do this. I don't know which ones exactly you want equal in width. This makes the final four columns of equal width using a new column type, H:

\documentclass{article}
\usepackage{array,calc}
\newlength{\origtabcolsep}
\setlength{\origtabcolsep}{\tabcolsep}
\newlength{\mycolswidth}
\settowidth{\mycolswidth}{\textbf{maximale Abweichung [\%]}}
\newlength{\mycolwidth}
\setlength{\mycolwidth}{.25\mycolswidth-.75\tabcolsep}
\newcolumntype{H}{>{\centering\arraybackslash}p{\mycolwidth}|}
\usepackage{booktabs}
\begin{document}
\begin{table}[htb]
\centering
\caption{Reproduzierbarkeit der Elektroden}
\setlength{\tabcolsep}{.75\origtabcolsep}
\begin{tabular}{*{5}{c}|*{4}{H}}
\toprule
\textbf{Elektrode} &\multicolumn{4}{c}{\textbf{Mittelwert [mV]}} &\multicolumn{4}{c}{\textbf{maximale Abweichung [\%]}} \\
\midrule
&pH 6 &pH 7 & pH 8 &pH 9 &pH 6 &pH 7 &pH 8&pH 9\\
\cmidrule[0.5pt]{2-9}
6 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
7 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
8 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
9 & 111 & 111 & 111 & 111 & 10 & 12 & 13 & 11\\
\bottomrule
\label{tab:reproduzierbarkeit}
\end{tabular}
\end{table}
\end{document}


-
That looks better, though the table is a bit wider than \textwidth, leading to an overfull box. (Sorry for being difficult to please.) Oh, and if you add \arraybackslash after \centering in the definition of H you can use \\  to start new table rows. –  Torbjørn T. Mar 16 '14 at 20:00
@TorbjørnT. Yes. I think it should be \tabcolsep rather than \arraycolsep. That helps a bit but I think there's some other spacing there I'm not getting. Thanks for pointing out \arraybackslash - that's a command I didn't even know to look for. –  cfr Mar 16 '14 at 20:10
@TorbjørnT. This version seems to avoid that at the cost of squeezing the tabular slightly. The overfull box is caused by the combination of array and the vertical lines since array allows them their natural width... –  cfr Mar 16 '14 at 20:28