Fractal dimension of the particles of powdered auxiliary substances expresses the raggedness of their surface, which can influence both the bulk density and their flow rate through the opening of the powder funnel. In the size fractions of 0.20–0.25 mmof six powdered auxiliary substances, their linear fractal dimensions within a range of 1.031 to 1.109 and the corresponding flow rates through the circular openings of the powder funnel of diameters of 6; 8; 10, and 12 mm were found. A significant correlation has been demonstrated between the flow rate expressed in volume (cm3/s) and the fractal dimension, which after an increase by one unit characterizes the surface of the particles.With increasing fractal dimension, the porosity of freely poured layer of powdered auxiliary substances is increased and simultaneously also their flow rate expressed in volume.For the usually reported flow rate expressed in weight (g/s), such influence is not significant.

        Key words: flow rate – bulk density – fractal dimension – auxiliary substances