X-ray computed tomography (CT) is increasingly recognized as a promising measuring technique for dimensional metrology. Various methods are being developed to improve measurement accuracy. Tests of new methods for such applications include accuracy evaluation with the use of calibrated workpieces; however, the internal algorithms of image acquisition and data processing might influence the experimental error, and then also the comparison of methods at different CTs. The accuracy of the results of tomographic measurements is influenced by many factors, one of which is the setting of the threshold value. The article presents the results of an attempt to use Monte Carlo simulated images to estimate deviations to determine threshold values to improve measurement accuracy and additionally, to estimate the impact of data processing. The differences of the results obtained from the simulated images were up to 4 % larger than those from tomographic images. It was caused by degradation of the image contrast by scattered radiation.