In method and module for calculation of an orthogonal x-ray attenuation of a subject using a measured reference x-ray attenuation in computed tomography, the reference x-ray attenuation and the orthogonal attenuation are provided as input quantities for an automatic dose control of the computed tomography apparatus. The positioning of the subject with regard to the rotation axis of the computed tomography apparatus is taken into account in the calculation of the orthogonal x-ray attenuation detection of the table height of the subject table.