This work presents a study of the relationship between the dynamic characteristics of a full-size structure and its scaled version. By understanding the similitude laws and suitably scaling material properties, one can utilize an efficient scale model to obtain realistic structural performance. The main goal is to identify whether the natural frequencies of a coupled fluid-structure system follow the same similitude law as the full-size structure and its scaled prototype. The coupled fluid-structure systems are those where the structural behavior affects the fluid response and the fluid behavior affects the structural response so both must be solved, i.e., coupled together, to obtain the interacting solution. Scaling of the structure in specific numerical analysis defines two models that are similar in their geometry and material properties and is considered only in relation to the need for laboratory testing of engineering models. The finite element representation of a laboratory tested physical model is a bridge between this small-scale prototype and the computational model of a real structure. A thin-walled water storage tank with a simple cylindrical geometry is adopted for the analysis as representative of a coupled fluid-structure system whose dynamic behavior is strongly influenced by the presence of fluid and neither the structure nor the fluid alone governs the response.