I have calculated the surface energy of a polymer using the following equation:

S.E.=(E_(Thin film)-E_(Amorphous cell))/2A

But what I found in the unit of kcal/mol/A^2.

Now I am converting the unit to mJ/m^2 by using N (Avogadro's no), n(number of molecules) and R (Repeat units).

Is this the correct procedure, or is there any other option for unit conversion?