This paper summarizes the results of a comparison on two calculable impulse voltage calibrators and one commercial calibrator between Helsinki University of Technology, Finland (MIKES-TKK), Nippon Institute of Technology, Japan (NIT), and Physikalisch-Technische Bundesanstalt, Germany (PTB). The peak voltage levels of the comparison ranged from 10 to 300 V. Both lightning and switching impulse voltage calibrators were studied using both positive and negative polarity impulses. The comparison was performed by applying impulses from the calibrators to a 12-b digitizer and then comparing the reported digitizer errors. For the switching impulse peak value, the agreement between the two calculable calibrators was better than 0.02% for all the measured voltages and better than 0.4% for the time parameters. For the lightning impulse peak value, the disagreement between the same two calibrators was smaller than 0.05% for all voltages examined and smaller than 1% for the time parameters.