Latex define o tamanho da mesa

\usepackage{booktabs}

\begin{table}[!htbp] % table环境
		\centering % 表示居中
		\begin{tabular}{|p{1cm}|p{2cm}|p{3cm}|}
			\hline
			a & b & c \\ 
			\hline
			d & e & f\\
			\hline
			g&g&i\\
			\hline
			j & k & l\\
			\hline
		\end{tabular}
\end{table}