A comprehensive testing program was carried out to compare the rheological properties of flowable concrete that can be obtained from different rheometers. The results obtained from seven rheometers using vane or similar geometries are discussed. A comprehensive flow curve analysis is undertaken for further comparison of the various rheometers. Partially, large differences could be observed between the results obtained from the different rheometers. However, the device-specific trendlines are shown to have significant correlations with the overall baseline. Two potential causes of differences between results are highlighted: imposition/registration of torque/rotational velocity and discrepancies between the measured material flow behavior in the device and the assumed ideal flow pattern. These differences can stem from a deviation from the perfect concentric cylinders system and bottom and top effects, in which the non-homogeneity of the material enhances these effects. It is shown that these effects are more dependent on mix design and rheological properties than on the testing devices. Also, the influence of extending the measuring procedure on measurement results is shown to affect the measured rheological properties of concrete and mortar. Finally, the paper serves as a comprehensive guide on how to interpret the rheological data and key factors that have to be considered during the analysis.