Abstract Finite-element impedance simulations were used to provide a relationship between the characteristic dimension and the physical dimensions of the interdigitated electrodes. Inclusion of electric and displacement currents allowed simulation of the capacitive loop associated with the geometric capacitance. An error analysis was used to quantify the influence of mesh and domain sizes on the numerical accuracy of the simulations. The interdigitated electrode geometry is shown to induce a frequency dispersion, dependent on electrode digit width, height, and separation, that can be characterized in terms of a complex ohmic impedance with real asymptotic limits for ohmic resistance at high and low frequencies. Characteristic dimensions, calculated from the primary ohmic resistance, the geometric capacitance, and the high-frequency ohmic resistance were in agreement for all geometries considered. The characteristic dimension calculated from the low-frequency ohmic resistance deviated under conditions that led to frequency dispersion. The Havriliak-Negami equation is shown to provide a good representation of the complex ohmic impedance. The present work is applicable to the analysis and interpretation of experimental data obtained using interdigitated electrodes.