With the difficulties to measure inter-particle distance in a suspension, the theoretical value under the several assumptions has been used. In this study, an image processing method for directly calculating inter-particle distances in a suspension was developed. This method enables inter-particle distances to be calculated regardless of the particle size, distribution, and morphology. A surface of suspension composed of particles and wax-polymeric binder was polished with acetone to expose the particles from the binder. The particles measured by scanning electron microscope were distinguished from the binder through the developed image processing method based on the intensity difference between the particles and binder. The inter-particle distances between the randomly selected particles and neighboring particles were calculated using the centroids and boundaries obtained by image processing. To determine the inter-particle distance as a representative value, a Monte Carlo method was employed. The inter-particle variation was defined to determine the iteration number for the Monte Carlo method. Finally, the inter-particle distances for the particle volume fraction of 40 and 50 vol% were obtained by the developed method. In addition, this developed method is available to describe the physical phenomenon such as a powder-binder separation and critical solid loading. (C) 2018 Elsevier B.V. All rights reserved.