Yttria-stabilized-zirconia samples with fairly narrow pore size distributions give well-defined microstructure impedance semicircles which can be characterized by a blocking factor alpha(R), a capacitance ratio alpha(C), and a frequency ratio alpha(F). On an alpha(R) vs. alpha(C) diagram, the regimes where either the pores or the grain boundaries are dominant are clearly separated. As expected from the reference model, the alpha(R) alpha(F) product was found proportional to porosity. The fairly continuous variations of alpha(F) from the densification to the grain growth regime revealed that voids remained present along the grain boundaries. Comparison of different results shows a remarkable constancy of the average thickness of the grain-boundary blockers in the samples sintered at high temperature. The electrical bulk properties obey simple laws as functions of porosity, which allows us to correct the conductivity and dielectric-constant data obtained with imperfectly densified materials.