The questions of calculating the calibration of the instrument cold rolling tube mills are discussed. A method of calculating the profile of a mandrel, consistent with existing caliber to ensure a more rational regime of reduction compared with the rolling process on the mandrel with a straight generatrix is proposed. The possibility of the use of existing calipers for the rolling of pipes, for example, more precise, using a mandrel, produced by the proposed method is envisaged. The proposed method is considered on the example of calculation of the profile of the mandrel caliber, a caliper which is calculated by the method of MISIS. The proposed method of calculating the calibration ensures a more even distribution of effort on the length of the work of the cone, and their reduction by 25 – 30 % and increasing the accuracy of tubes in comparison with the traditional method.