In this work, we first adapted the Gouy-Chapman-Stern model for bulk water-in-LiTFSI electrolyte by incorporating ionicity into the calculation of the Debye length, i.e. the diffuse layer thickness. The trend of the EDL capacitance as a function of the electrolyte concentration using the modified expression for the Debye length closely matches the values obtained from electrochemical impedance spectroscopy (EIS). Likewise, the trend of the diffuse layer thickness aligns with the experimental differential capacitance. We used a commercial carbon containing micro-and mesopores to comprehend the screening length in the pores. Rather than using complex models, we simply divided the Debye length in the bulk solution by the MacMullin number, i.e. the ratio of tortuosity to porosity, to differentiate the Debye length distribution in micro-and mesopores. Furthermore, introducing the MacMullin number into the Stokes-Einstein equation enabled the estimation of ionic radii within pores, which was subsequently used to determine ion desolvation in micro-and mesopores. Our findings reveal that ion association governs the Debye length trends in pores, aligning precisely with patterns of confined ionic radii, desolvation, and resulting EDL structure.