The limit below which the magnetization curve of a mesoscopic superconducting prism of square cross-section and finite height approximates the characteristic bi-dimensional limit, e.g. long prism, which with both the magnetic induction and the superconducting electron density are invariant along the direction where the magnetic external field is applied, was numerically found. Using the three- and two-dimensional time-dependent Ginzburg–Landau models, we have determined an analytical dependence of this height limit as a function of the lateral size of the sample.