The dimension of ( 1/2) ${\mathrm{\epsilon }}_0$E² ( ${\mathrm{\epsilon }}_0$: permittivity of free space; E : electric field) is :

  Energy per unit volume = energy density due to electric field =$\frac{E^2{\in }_0}{2}$

                                                                                                 =$\frac{M L^2{T}^{-2}}{L^3}= M L^{-1}{T}^{-2}$