Measuring shape errors on coordinate measuring machines is a process that is widely used nowadays due to the ease and speed with which the results of a given characteristic can be obtained. The aim of this work was to establish a rule for determining the minimum number of points to be touched when measuring the roundness of various parts. For the case study, measurements were taken on a part manufactured exclusively for this work, where the initial objective was achieved through calculations and comparisons. Based on the results of the measurements, a rule was defined which consists of touching 1 point/mm of the calculated perimeter, considering the nominal diameter specified in the drawing. The use of the rule allows for greater confidence in the results obtained, as it establishes a standard for circularity measurements in various diameters and a reduction in measurement costs, as the time spent on this process is considerably reduced (72.9% in the case studied) depending on the number of points chosen by the metrologist.