the formula to calculate the capacitance is

C = (ε A)/d

where ε is dielectric absolute permittivity
A is the overlap area in what units?
d is the distance between the plates in meters

what is the formula to use the relative permittivity instead?

Thank you

 

A is the overlap area in what units?

area is measured in square metres in the MKS (ISO) system.

 

> A is the overlap area in what units?
> d is the distance between the plates in meters

Since you will measure d in meters, to be consistent, you
need to measure A in square meters.

> what is the formula to use the relative permittivity instead?

Write \(\epsilon = \epsilon_{rel} \epsilon_0\), where
\(\epsilon_{rel}\) is the relative permittivity (a.k.a.
dielectric constant) and \(\epsilon_0\) is the vacuum
permittivity (which equals \(8.85 \times 10^{-12} \, F/m\)).