It is well-known that rocks have heterogeneous properties, and these properties played a curial role in blasting operations to obtain fragmented rocks with different particle size distributions. Therefore, the estimation of the particle size distribution of the rock is one of the most important parameters in terms of the economic operation of open-pit mines as it is directly related to mining operations such as loading, transporting, crushing, and grinding. Many parameters divided into controllable and noncontrollable affect the efficiency of blasting operations. This study aimed to suggest new empirical models based on nondestructive test methods including P wave velocity and Schmidt hardness to predict the mean particle size of the rock after blasting. WipFrag software was used to evaluate the pictures taken after blasting and to determine the average particle size distribution of the rock mass. Experimental results obtained from simple and multiple regression models show that there is a good agreement observed between the mean particle size of rock mass and its Schmidt hammer hardness and P wave velocity properties.