A new formula describing size effect was proposed. This formula has a form
where  is the nanoparticle radius and  is wave number. It is supposed here that the time dependence of the electromagnetic field is given by the factor  In this paper Bruggemans approach was used, but electromagnetic field for electric-dipole oscillation mode inside the picked particle was computed without applying quasi-static approximation. Thus the function  is due to the field nonuniformity inside the picked particle. In quasi-static region (, i.e.  for Ag this function becomes constant  and formula (5) becomes identical with Bruggemans formula.