Using the module *xrefit*, structures can be fitted to available *rotational constants* as obtained from the analysis of *rotational* or *rovibrational spectra*. The structure is obtained using a least-squares fit using either the rotational constants or the corresponding moments of inertia (with appropriate weights). The fitting program in addition allows to subtract *vibrational corrections* (obtained for example in quantum chemical calculations of the cubic force field) and to consider the *electronic contribution* (as obtained in quantum-chemical calculations of the rotational g-tensor) and in this way to provide the *equilibrium structure* of a molecule.