Liquid atomization is a largely widespread unit operation. The disintegration of a liquid into droplets depends on the nature of the nozzle, on the process parameters as well as physicochemical characteristics of the fluid. The aim of this work is to study the contribution of the process (liquid outlet speed and air pressure) and physicochemical (viscosity and surface tension) factors on the size distribution of droplets generated by single- and two-fluid flat spray nozzles. The obtained droplet median diameters which range between 77 and 594 mu m for the single-fluid nozzle and between 11 and 599 mu m for the two-fluid nozzle, are discussed in relation with operating conditions of atomization process. Dimensional analysis was performed as a modeling approach. Despite energy input for the droplet formation is known to be influenced by different origins according to single and two-fluid nozzles, it is shown that a unique correlation, with specific values of parameters for each nozzle type, gathers all the parameters affecting droplet size. In the range of process and formulation parameters tested, this correlation is validated and gives satisfactory agreement for the single- and two-fluid nozzles. (C) 2012 Elsevier B.V. All rights reserved.