We have fabricated a large body of pentacene thin films on different organic and inorganic dielectric materials at four substrate temperatures with different nominal film thicknesses ranging from the submonolayer over the multilayer to the “thick” film regime. These films were characterized by atomic force microscopy and analyzed quantitatively by means of scaling and rate equation theory in order to deduce the molecular growth dynamics of pentacene films on organic substrates that are used as gate dielectrics in organic thin film transistors. We found that on all substrates and in the substrate temperature range $25°\mathrm{C}⩽T_s⩽70°\mathrm{C}$ the growth can be well described as diffusion-limited aggregation. A critical island size of $3⩽i⩽4$ was deduced from the scaling of the distribution density of the pentacene grain areas and the power-law dependence of the saturated nucleation density on the deposition rate. This is valid for all substrates in the investigated temperature regime and is also found to be true for $50\mathrm{nm}$ thick pentacene films thus emphasizing that the molecule-molecule interaction itself is independent of the underlying surface.