  Ferroelectric nematic liquid crystals are currently being subject to a
plethora of investigations since they are of great fundamental interest and
could potentially foster promising applications. However, many basic aspects
are still poorly understood, among which the problem of the dielectric constant
stands out. Ferroelectric nematics exhibit giant dielectric constants whose
value depends on the thickness of the measurement cell. Even though this must
be the result of a spurious artifact, the intrinsic permittivity has not been
determined yet. In this work, we tackle this problem by modeling the dielectric
response of the liquid crystal filled cell through an equivalent circuit
accounting for polarization reorientation and the effect of insulating
interfacial layers. We arrive at the conclusion that the perpendicular
component of the permittivity $\varepsilon_{\perp}$ is of the order of $10$ in
the prototypical ferroelectric nematogen DIO, while the parallel component
$\varepsilon_{\parallel}$ is of the order of $150$. In this way, the dielectric
tensor of DIO has been fully determined.
