This study shows that the resolution of a digital elevation model (DEM) and model mesh strongly influences 3D simulations of seismic response. Topographic heterogeneity scatters seismic waves and causes variation in seismic response (amplification and deamplification of seismic amplitudes) at the Earth’s surface. DEM resolution influences the accuracy and detail with which the Earth’s surface can be represented and hence affects seismic simulation studies. Apart from the spatial resolution of a DEM, the mesh resolution, adopted in the creation of a 3D spectral element meshing, also changes the detailedness of surface topography. Working with high‐resolution data is in most cases not possible on a regional scale because of its costliness in terms of time, money, and computation. In this study, we evaluate how low the resolution of DEM and mesh can become before the results are significantly affected. We simulated models with different combinations of DEM and mesh resolutions. The peak ground displacement (PGD) obtained from these simulations was compared with the PGD of the model with the finest mesh and DEM resolution. Our results show that any mesh or DEM resolution of 540 m or coarser will give unrealistic results. These results are valid for similar terrains as studied here and might not be directly applicable to regions with significantly different topography.