A laboratory experiment for the determination of the cross-linking density of silicone elastomers is described on the basis of swelling experiments and mechanical tests. In the experiment, the macroscopic swelling and mechanical behaviors of the elastomers were discussed as a function of the cross-linking density, which can be easily controlled by varying the base-to-curing-agent ratio during elastomer synthesis. The cross-linking density and the average molecular weight between cross-links were calculated from the swelling degree at equilibrium through the Flory-Rehner theory and from a simple mechanical model. The results have shown a good convergence of the average molecular weight between cross-links calculated from the two methods, respectively. On a more general note, the suggested experiments and the associated results offered numerous opportunities for discussions on macromolecular architectures, interactions between polymers and solvents, and mechanical properties of elastomeric materials.