In this paper, we propose a simple and intuitive way to predict self-assembled island sizes for varying deposition conditions, i.e., temperature and deposition rate. The average island size and the modality of the size distribution (unimodal with large or small islands, or bimodal) is calculated via materials balancing over a total island density (known by experiments or from nucleation calculations). We also find that there is a density interval in which the size distribution is bimodal. The width of this interval increases with the total amount of material in the islands. The borders of the interval change with the sizes of the small and large islands, which can also change the interval width. (C) 2002 Elsevier Science B.V. All rights reserved.