The capacitance of a capacitor with vacuum (or free space) or medium having distance between the plates d is:
C = \(\frac{ɛ_oA}{d}\).............................(1)
We know that, a dielectric of dielectric constant K and thickness t is equivalent to thickness \(\frac{t}{K}\) for vacuum of free space.
So total equivalent vacuum separation of the plates of the capacitor will be: