I was searching here to find a way to change the font size from normal to \footnotesize for the longtabu tables. However, the answer in longtable question didn't work in my case. They made corrections for scriptbook style.
Basically, the question is the same: I want to change the font size of the main text in table without changing the caption size. Here is the example I tried to use what have been suggested: {\footnotesize ... } But it makes the caption footnotesized.
Here is the MWE:
\documentclass[12pt,oneside]{report}
\usepackage{tabu}
\usepackage{longtable}
\usepackage{booktabs, multicol, multirow}
\begin{document}
\chapter{Minimum Working Example}
Composition of samples
{\footnotesize
\begin{longtabu} to \linewidth{X[l3.0] X[c] X[c] X[c] X[c] X[c]}
\caption{Composition of samples} \\
\toprule
\textbf{Component} & \textbf{Text1} & \textbf{Text2} & \textbf{Text3} & \textbf{Text4} & \textbf{Text5} \\
\midrule
H$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
O$_2$ & 0.38 & 0.10 & 0.30 & 0.91 & 0.99 \\
C$_1$ & 11.98 & 11.30 & 10.98 & 11.94 & 11.09 \\
C$_2$ & 0.44 & 0.39 & 0.43 & 0.91 & 0.33 \\
N$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
S$_2$ & 0.81 & 0.81 & 0.81 & 0.11 & 0.83 \\
C$_3$ & 9.19 & 9.01 & 9.10 & 9.84 & 9.18 \\
H$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
O$_2$ & 0.38 & 0.10 & 0.30 & 0.91 & 0.99 \\
C$_1$ & 11.98 & 11.30 & 10.98 & 11.94 & 11.09 \\
C$_2$ & 0.44 & 0.39 & 0.43 & 0.91 & 0.33 \\
N$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
S$_2$ & 0.81 & 0.81 & 0.81 & 0.11 & 0.83 \\
C$_3$ & 9.19 & 9.01 & 9.10 & 9.84 & 9.18 \\
H$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
O$_2$ & 0.38 & 0.10 & 0.30 & 0.91 & 0.99 \\
C$_1$ & 11.98 & 11.30 & 10.98 & 11.94 & 11.09 \\
C$_2$ & 0.44 & 0.39 & 0.43 & 0.91 & 0.33 \\
N$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
S$_2$ & 0.81 & 0.81 & 0.81 & 0.11 & 0.83 \\
C$_3$ & 9.19 & 9.01 & 9.10 & 9.84 & 9.18 \\
H$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
O$_2$ & 0.38 & 0.10 & 0.30 & 0.91 & 0.99 \\
C$_1$ & 11.98 & 11.30 & 10.98 & 11.94 & 11.09 \\
C$_2$ & 0.44 & 0.39 & 0.43 & 0.91 & 0.33 \\
N$_2$ & 3.94 & 3.81 & 4.03 & 3.88 & 4.01 \\
S$_2$ & 0.81 & 0.81 & 0.81 & 0.11 & 0.83 \\
C$_3$ & 9.19 & 9.01 & 9.10 & 9.84 & 9.18 \\
\bottomrule
\end{longtabu}}
\end{document}
tabu
tomultirow
should already be enough here. Do you want all tabus or all longtabus or just this one to be scriptsize?