\documentclass{article}
\usepackage[np]{numprint}
\begin{document}
\pagestyle{empty}
\renewcommand {\arraystretch }{1.5}
\begin{tabular}{|l|*{3}{w{c}{10mm}|}}
\cline{1-4}
longueur initiale & \numprint[cm]{3} & \numprint[cm]{4} & \numprint[cm]{5}\\
\cline{1-4}
longueur agrandie & & \numprint[cm]{4.8} & \\
\cline{1-4}
\end{tabular}
\end{document}