X-ray computed tomography (XCT) is uniquely suitable for non-destructive dimensional measurements of delicate or internal features produced, for example, by additive manufacturing. While XCT has long been used in medical imaging, it has been used for industrial dimensional measurements only in recent years. The error sources in XCT of industrial components is still a topic of active research. One subgroup of potential error sources in XCT measurements are uncorrected XCT instrument geometry errors, such as detector misalignment or rotation stage errors, and are the focus of this paper. We demonstrate the effect of some instrument geometry errors on measurements performed on a calibrated artifact and compare the results to those obtained through simulations. The overall objective of this work is to support ongoing efforts to develop documentary national and international standards for performance evaluations of XCT instruments. In this study, we focus on cone-beam XCT instruments.