A microlluidic diffusion chamber with 3 inlets and a circular central chamber allows a 2D concentration gradient to develop. This diffusion chamber has been characterised numerically for the effect geometry has on equilibrium time, the concentration profile and the flow profile within the central chamber. As the Einstein-Smoluchowski relation predicts, the time to reach steady state is proportional to the square of the radius of the chamber but features within the chamber are qualitatively insensitive to the size of the chamber within the range of 100-1000 mu m. Inlet width had a much more significant effect on the qualitative behaviour within the chamber, affecting the symmetry of the concentration profile. It is recommended that inlet widths are less than 80 mu m to preserve symmetry. In this paper, the effect of geometry on both transient and steady-state behaviour has been explored, providing a basis and criteria for designing chambers for a wide range of applications, including studying the effect of concentration gradients on cell mobility or a rapid assay for biofilm development in a range of concentrations. (C) 2014 Elsevier Ltd. All rights reserved.