The composition of the powder-binder mixture (feedstock) used in powder injection molding (PIM) plays a crucial role in fabricating defect-free parts. Powder-binder separation in the feedstock during mixing or molding is responsible for defects such as voids, cracks, or distortion in the sintered part. This study introduces an inter-particle spacing parameter, 6, based on particle size (D), particle volume fraction (phi) and maximum particle fraction (phi(m)). The derived parameter is investigated using feedstocks prepared from three different metal powders. Based on comparisons with experimental data from this study as well as reports in the literature, the inter-particle spacing parameter, 6, proves to be a useful predictor of powder-binder separation. The newly proposed parameter assists in designing and developing feedstocks to manufacture components by PIM. (C) 2013 Elsevier B.V. All rights reserved.