The time dependence of the domain switching current density, J sw ( t ), under pulsed voltages on a ferroelectric parallel-plate capacitor is the consequence of region-by-region polarization reversals across the fi lm. As the distributive coercive voltage of domain nucleation increases from zero to the maximum applied voltage during the capacitor charging time, J sw ( t ) is proportional to the domain switching speed at each time. By transforming the spatially inhomogeneous domain nucleation distribution into a temporal distribution of coercive fi elds ( Ec), a local ln J sw versus E c−1 plot is derived for each domain, following the Merz equation. This provides insight into the independent domain switching dynamics at different nucleation sites in Pb(Zr0.35Ti0.65) O3 thick fi lms over a large current range. Although the activation fi eld of the slope of the ln J sw ( t ) versus E c − 1 plot varies with fi lm area and temperature, all the plots extrapolate to a single point ( Jo, Eo) from which the ultimate domain switching current density of J 0 = 1.4 × 10 8 A cm − 2 at the highest fi eld of E 0 = 0.20-0.25 MV cm − 1 is derived. Unexpectedly, J 0 and E 0 are independent of the film thickness and area, after correction for a small interfacial-layer effect. This analysis provides rigorous evidence for nucleation rate-limited domain switching with a subpicosecond nucleation time and the relative unimportance of domain forward-growth time across fi lm thicknesses between 0.14 and 2 μ m. This work paves the way to improve the effi ciency of ferroelectric thick-film functionality in electronic and optoelectronic devices with ultrafast clock rates.