Abstract: The ring radii and cavity radii of 12-crown-4,15-crown-3,18-crown-6,2l-crown-7,24-crown-8,27-crown-9 and 30-crown-10 as well as the distances between metal ions and oxygen atoms on the ring are calculated on the basis of an "Atoms-in Coniact"model. Most of the values thus obtained are in good agreement with earlier estimates based on other models or deduced from X-ray crystallographic data.It is therefore possible to nake predictions on the stability of certain crown complexes,the molecular geometry of which has not been clear thus far.