This work demonstrates a simple means of predicting aerodynamic diameter of particles having fractal surfaces. A number of drag coefficient expressions were employed for the calculation of aerodynamic diameter. A set of model objects having surface fractal dimensions varying from 2.00 to 2.55 was constructed, from which all the parameters required to compute shape and surface roughness factors can be obtained. Drag coefficients (CD) formulated by Ro and Neethling, Haider and Levenspiel, Thompson and Clark, Ganser, and Tran-Cong et al. were shown to perform similarly within the specified criteria. The aerodynamic diameters calculated follow the expected trend of decreasing diameter with increasing surface roughness. Comparisons with literature data show that the CD expressions by Ro and Neethling, Haider and Levenspiel, and Ganser, on average, agree to within 17-23% of the measured values. (C) 2004 Elsevier B.V. All rights reserved.