In performance-based seismic design the global displacement capacity of structures is predicted on the basis of local engineering demand parameters and mechanical models that link local and global deformation quantities. Although unreinforced masonry (URM) is one of the most used construction materials for residential structures all over the world, the displacement capacity of in-plane loaded URM walls is still mainly estimated from empirical drift capacity models rather than mechanical relationships between local and global deformation capacities. In this article, we present an analytical model which links the top displacement of an URM wall to the applied in-plane shear load. In order to verify the model, we compare the predicted results to global and local deformation quantities from own URM wall tests. Comparison of global deformation quantities shows that we are able to predict the initial stiffness of the walls with the simple assumption of a no-tension material and a linear-elastic material in compression. For walls developing a diagonal shear failure or hybrid failure, the predicted force-displacement curve starts diverging from the experimental envelope with the formation of the first diagonal cracks. With comparison of local deformation quantities, e.g. curvature profiles and shear strain profiles, we show that this is due to the formation of a significant diagonal shear crack.