In this paper, it is shown that the concentration of the colloidal suspension has a significant role in the assembly of a uniform centimeter-sized monolayer colloidal crystal (MCC) and the optimized range of the concentrations for fabricating MCCs made of polystyrene (PS) microspheres with the diameter of 508 nm is obtained. The gravity assisted convective assembly method is used to fabricate MCCs. It has been shown that not only the size of the MCC but also its uniformity and quality is highly dependent on the concentration of the colloidal suspension. Having used different methods to analyze the samples such as taking the transmission spectra, optical microscopy imaging, scanning electron microscopy (SEM) imaging, and studying the diffraction patterns of the samples, it is deduced that the optimized range of the concentration is from 1.7 wt% to 1.85 wt%. (C) 2017 Published by Elsevier B.V.