The activation energy for atom diffusion across steps and facets is a key factor in the surface structure formation during thin films deposition processes. In this work, we calculate facet-facet barriers for atom diffusion of small Cu clusters (up to eight atoms) from {1 1 1} facets to {1 1 1} (or {1 0 0}) facets. In each case we focus only on the atom-by-atom diffusion process because this mechanism was previously found as being energetically the most favourable. Our results show that, for all clusters considered, the diffusion barriers become independent of the facet size for three or more atomic layers. In addition, clusters bigger than trimers present similar lowest facet-facet barriers, except for heptamers which present the highest activation energy. In general, for single steps, diffusion from {1 1 1} to {1 1 1} presents smaller lowest and highest energy barriers than diffusion from {1 1 1} to {1 0 0}. But for multiple steps (facets), both cases show similar behaviours. Finally, it is worth noting that all these barriers are significantly greater than the corresponding concerted cluster diffusion over a plane. © 2007 IOP Publishing Ltd.