Resin films based on polyurethane dispersions (PUDs) have recently gained substantial interest as surface protective coatings. However, defects in the resin films such as micro-cracks may induce high permeability to moisture, thereby compromising the coatings' performance. In this contribution, we report on a simple electrochemical method for characterization of the micro-cracks in a resin film deposited on a copper surface. Electrochemical measurements are facilitated in a two-electrode cell where the resin-coated copper electrode serves as the anode. The ionic current flow due to electrolyte penetration within the micro-cracks of the resin film is measured and quantified. The ionic current (I) exhibits an inverse exponential dependence on the film thickness (x): I ae e(-x) . The physical basis for this dependence is discussed using a mathematical model that incorporates the surface fraction of micro-cracks in a layered resin film. While the analysis presented herein is for the specific case of PUD resins, the overall methodology is applicable to the characterization of many metallic and non-metallic surface coatings used in corrosion protection and surface functionalization applications.