In natural stone processing plants, natural stone blocks are cut into slabs of different thicknesses for flooring and cladding applications. However, products of the desired dimensions may not be obtained, as they can be broken or and fractured into pieces of various sizes during the cutting and dimensioning process due to structural defects. The slab efficiency of a stone block that is, the percentage of the slabs produced from the block that are of the desired size-depends mainly on the structural quality of the block. Therefore, it is important to assess the structural quality of blocks before the cutting process. In this research, P-wave velocity measurements were performed on 105 large blocks, including seven different natural stone types. After the cutting process, the slab efficiency of each block was determined. Upon analyzing the results, it was found that it is possible to predict the slab efficiency for an uncut natural stone block from its average P-wave velocity value. Additionally, it was shown that the slab efficiency can be enhanced by determining the optimal cutting direction based on the P-wave velocity contours inside the block.