This study investigates the influence of particle size distribution (PSD) width on the internal friction and internal pressure ratio of granular materials, and the related flowability of such material when uniaxially compressed in a closed volume. For this purpose, an optical granular friction analyzer (O-GFA) was used to evaluate the granular friction analyzer (GFA) index, which may be related to the internal friction and internal pressure ratio. By examining bronze powder samples with 3 different PSD widths it was shown that as PSD width increases, the load independent GFA index increases, internal friction decreases and the internal pressure ratio remains constant. Furthermore, our study confirms that, determining the GFA index using the O-GFA for characterizing the flowability of uniaxially compressed granular material is an alternative to traditional methods, which require the individual properties of granular materials i.e. internal friction and internal pressure ratio to be determined through two separate tests. (C) 2020 Elsevier B.V. All rights reserved.