Significant efforts have been made by materials scientists and metallurgists to understand the underlying physics involved in solidification of aluminum alloys to predict a variety of casting defects. Shrinkage porosity is one of the most important types of casting defects. Addressing porosity has been a formidable challenge due to many contributing (and interacting) phenomena responsible for its formation and growth. Shrinkage porosity occurs by nucleation and growth phenomena. Very few previous models for shrinkage prediction consider the pore formation based on a nucleation and growth basis. Several models that can predict micro shrinkage in castings were revised in detail. The main purpose of this study was to develop a comprehensive model which can predict micro-shrinkage pores that are forming during solidification of A356 castings. The model utilizes a stochastic approach and takes into consideration the Niyama criterion as well as the nucleation potential for formation of pores. Therefore, it can predict the random nature of pore formation during casting solidification. Correlations between the predictions and the pore amount were developed. For this model, literature validation was provided for an A356 alloy plate casting. Further validation was performed for a bar geometry cast in a silica sand mold. The model predictions match reasonably well with the experimental pore distribution profile.