What will be the energy density in a Parallel Plate capacitor?

The symbol to represent energy density is (u).So it is the total energy stored in the capacitor per unit volume.

So according to the above definition its equation will be:

U= Total Energy(U)/ Volume(v)= ½ CV ²/Ad
Using C =A/d and V=Ed.
Now from the above equations we get :
U= A / 2d * E²d /Ad = ½ * E² ——— 2.18