This program is based on Table 2H of IEC 60950. Select the Insulation, Pollution Degree, Nominal AC Mains, and enter the Working Voltage (peak or dc), then click on the button to get the corresponding Clearance in mm and mils.
Interpolation Note: This calculator performs linear interpolation between 2800 V peak or d.c. and 42000 V peak or d.c. per Note 3 of Table 2H. Please note that this calculator only covers Table 2H. I'm working on a version that will include Tables 2J, 2K, and the alternate method in Annex G.