[Tex/LaTex] Table cell text overflow when using \multirow

cellline-spacingtables

I have made a table and in it, I have to use the multirow package for the headers. Works fine when there are two lines but it y-overflows when there are three. I tried increasing the space in each row with \setlength\extrarowheight but that just increased the cell and the overflow remained.

Here are a few pictures:

Table image, source code shown below

How do I solve this?

Here is the source for the table:

\documentclass[11pt,a4paper]{article}
\usepackage{multirow}
\begin{document}
\begin{table}[h!]
    \centering
        \caption{OVERFLOW}
        \bgroup
        \def\arraystretch{1.5}%
            \begin{tabular}{|c|c|c|c|c|c|c|c|}
            \hline
            \multirow{2}{*}{
                \begin{tabular}[c]{@{}c@{}}Extension\\
                $x/\mathrm{cm}$\end{tabular}} & 
            \multicolumn{5}{c|}{
                \begin{tabular}[c]{@{}c@{}}Distance travelled \\
                $s_{i}/\mathrm{cm}$\end{tabular}} & 
            \multirow{2}{*}{
                \begin{tabular}[c]{@{}c@{}}Avg. distance\\
                $s/\mathrm{cm}$\end{tabular}} & 
            \multirow{2}{*}{
                \begin{tabular}[c]{@{}c@{}}Uncertainty in\\
                avg. distance\\ $\Delta s/\pm \mathrm{cm}$\end{tabular}} \\ 
                \cline{2-6} & 
            Trial 1 & Trial 2 & Trial 3 & Trial 4 & Trial 5 &  &  \\ 
            \hline
            \end{tabular}
        \egroup
    \end{table}
\end{document}

Best Answer

Edit:

With using makecell package for define multi-line multi-row cell, I obtain:

enter image description here

In table instead to increase \arraystretch I use gaped cells from makecell package:

\documentclass[11pt,a4paper]{article}
\usepackage{makecell, multirow}
\usepackage{siunitx}

\begin{document}
    \begin{table}[h!]
    \centering
\caption{OVERFLOW}
\setcellgapes{5pt}
\makegapedcells

\begin{tabular}{|c|c|c|c|c|c|c|c|}
\hline
\multirowcell{3}{Extension\\ \si{x/cm}}
    &   \multicolumn{5}{c|}{\makecell{Distance travelled \\ \si{s_{i}/cm}}} 
        &   \multirowcell{3}{Avg. distance\\ \si{cm} } 
            &   \multirowcell{3}[1ex]{Uncertainty in\\
                                      avg. distance\\ 
                                      \si{\Delta s/\pm cm}}}  \\
        \cline{2-6} &
    Trial 1 & Trial 2 & Trial 3 & Trial 4 & Trial 5 &  &  \\
    \hline
    \end{tabular}
    \end{table}
\end{document}
Related Question