Within the scope of an international pilot study on the "Calibration of piston-operated pipettes with air cushion", the influences on the measurement uncertainty budgets have been extensively analysed. This pilot study was carried out as a laboratory comparison between twelve calibration laboratories which are accredited according to ISO/IEC 17025:2005, and one National Metrology Institute. As calibration objects, piston-operated pipettes from different manufacturers were used. Starting from the comprehensive calibration results, statistical methods for the determination of the reference value and of the attributed measurement uncertainties were applied. The mean value of the measurement results was selected to define the reference value, establishing the basis for the comparability of the measurement results of the participants. The standard deviation was used as the measurement uncertainty of the reference value and was found to lie within the tolerance limits according to standard EN ISO 8655 and the different manufacturers’ specifications. The evaluation of the measurement results led to a more accurate estimation of previously known measurement uncertainty contributions as well as to the identification of new contributions to the measurement uncertainty budget. Derived from this, the calibration procedures and the measuring conditions were specified or determined to ensure national and international comparability.