Breakdown voltage of insulators is strongly affected by atmospheric conditions such as temperature and humidity. Since the insulators are usually used at different atmospheric conditions from the test condition, it is essential to use a correction factor to obtain the real breakdown voltage from the test results. On the other hand, lack of a specified correction factors for measuring flashover voltage of insulators in IEC60060-1(2010), which are necessary for giving certification, enhances the need of more studies to be done on breakdown voltage of insulators. In this article we surveyed the validity of applying IEC sparkover atmospheric corrections to insulators flashover. We have tested 17 of 20 kV insulators comprised porcelain, glass, and composite with different arcing distances at varying atmospheric conditions. The corresponding humidity varied homogeneously from 1 gm/m 3 to 13 gm/m 3 in the 6*4*3.3 m testing room. Using the IEC humidity correction factors, the breakdown voltages measured in test conditions were turned into the voltages corresponding to standard conditions in order to make it possible to verify the accuracy of IEC humidity correction factor equations. Results obtained from comparison show that there should be more studies to find appropriate correction factors for flashover voltages like the ones done for sparkover voltages.