The speed of electromagnetic waves in vacuum is equal to 

According to Maxwell, it is found that the electromagnetic waves travel in free space (or vacuum) with a speed which is given by   $c=\frac{1}{\sqrt{{\mu }_0{\epsilon }_0}}=3\times {10}^8{ \mathrm{ms}}^{-1}$

where,  ${\mu }_0\left(=4\pi \times {10}^{-7} \mathrm{Wb}{ \mathrm{A}}^{-1}{ \mathrm{m}}^{-1}\right)\text{ and }{\epsilon }_0$

$\left(=8.85\times {10}^{-12}{\mathrm{C}}^2{ \mathrm{N}}^{-1}{ \mathrm{m}}^{-2}\right)$  are absolute permeability and permittivity of the free space, respectively.