The principles for estimation of the patient's radiation dose from conventional radiographic and computed tomography examinations are presented on the basis of published exposure simulation data. The relationship between absorbed dose in air, or axis dose, organ doses, and effective dose is explained. It is shown how organ doses can be calculated from the absorbed dose free in air or axis dose using published computed conversion factors. Calculation of the effective dose from organ doses using tissue weighting factors is described. Finally, examples of dose calculation are given for a conventional radiographic and a CT examination.