In this paper, the Weibull distribution is employed to characterise the surface topography in the analysis of the passive intermodulation(PIM) between rough circular waveguide flanges, where the PIM level as a function of different system parameters such as the applied pressure, roughness, layer thickness and the power ratio has been developed assuming that the PIM level for a particular set of parameters is known. The proposed method is more significant when the contact surface needs to be described by parameters like the skewness or the kurtosis.