Abstract When reporting electrochomic (EC) properties, it is required to give a quantitative measure of the intensity of the color change. Even though the transmittance difference (Δ T ) between the two states has been used widely, many researchers tend to find out the maximum EC contrast (Δ T max ) and the corresponding thickness ( L m ) of an EC material on a trial-and-error basis. In this article, we propose a very convenient and systematic method to predict the Δ T max and the L m of an electrochromic material. These quantities are material characteristics, which are independent of the device. In order to demonstrate the usefulness of the method, we carried out EC experiments using a well-known EC polymer, poly(3,4-ethylenedioxythiophene) [PEDOT]. PEDOT was prepared by electropolymerization of the corresponding monomer in a potentiodynamic mode. The film thickness was controlled by varying number of sweep cycles. The Δ T max of PEDOT was estimated to be 48.2% at ca. 3 cycles in the case of 0.02 M PEDOT solution. We believe that the systematic approach can also be applied to variety of coating processes in the EC device fabrication.