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The classical nucleation theory provides a rate equation for the emerging embryos of a new phase. The standard form of homogeneous nucleation rate J can be written as,

(2.6)

where J₀ is a pre-exponential factor, which depends on the rate at which molecules strike a unit area of the embryo surface. For homogeneous nucleation of water, including condensation and icing, J₀ can be expressed as,

(2.7)

in which, c_sat,2 is the concentration of water molecules at saturation with respect to the new phase, w^↓ is the flux of water molecules to the nucleus surface.

Despite its simplicity, the classical nucleation theory provides a remarkably good prediction for most materials in a certain range of temperatures. Though the theoretical temperature dependence of J is usually higher than that found in experiments, various correction functions have been developed to modify the classical model and bring it into better agreement with the experimental observations [89-91].