We have determined new statistical relations to estimate the fundamental atmospheric parameters of effective temperature and surface gravity,using MK spectral classification,and vice versa.The relations were constructed based on the published calibration tables(for main sequence stars)and observational data from stellar spectral atlases(for giants and supergiants).These new relations were applied to field giants with known atmospheric parameters,and the results of the comparison of our estimations with available spectral classification have been quite satisfactory.