In the domain of ceramic additive manufacturing, sintering is a key step for controlling the final shape and mechanical strength of a 3D object. The thermal treatment of the printed green objects has a high influence on the specimen density, debinding, and sintered microstructure. This work focuses on the shrinkage anisotropy phenomenon that occurs during sintering. We demonstrate by dilatometry and interrupted sintering microstructure analysis that this phenomenon originates from non-ideal particle packing between the printed layers, which generates an anisotropic porosity distribution at the mesoscale. Based on this, a sintering model is developed and specially adapted for the numerical prediction of the sintering anisotropy. This model is formulated in analytic equations that can easily identify all the model parameters and reproduce the experimental dimensional changes. This numerical tool can be of great assistance in the prediction of additive manufacturing object dimensional changes during sintering.