During injection molding process melted polymer is introduced into mold cavity due to the pressure delivered from injection unit. The amount of pressure needed to inject polymer melt into cavity depends on many aspects, especially: polymer properties, runner geometry, cavity geometry and processing parameters. Mold design principles suggests that filling of the cavity should be balanced. It means that the furthest regions of cavity (measured from injection point) should be filled at the same time to avoid problems with differential shrinkage and injection pressure drop. In this paper the relation between fill imbalance and injection pressure needed for cavity filling were investigated with Autodesk Moldflow Insight software. In this research several different shapes and shape modifications along with thickness change of analyzed parts were performed to measure the significance of imbalance on injection pressure drop. Simulations with three different polymer grades were performed to estimate the influence of material properties on pressure drop when fill imbalance occurs.