Simulations based on the discrete element method (DEM) are used to investigate the relationship between the distribution of particle sizes and the macroscopic sintering behavior of ceramic powders. This is achieved by generalizing the DEM force laws for solid-state sintering in such a way that sintering of particles with different sizes can be simulated. A generation scheme for initial particle packings with realistic physical properties is presented, which allows for different distributions, ranging from monomodal to normal, log-normal, and bimodal distributions. It is shown that the type and width of the distribution has a significant effect on the strain rates and viscosity during sintering. Broader size distributions lead to reduced sintering rates, although particle rearrangement is enhanced. However, the accelerating effect of rearrangement is overcompensated by an increase of the contact area between particles when the size distribution becomes wider. The simulation results are in good agreement with experimental results on a commercial Al2O3 power.