The paper presents the analysis of 3D particle shape on three-grain fractions of a calcareous sand based on the raw data of X-Ray computed tomography (X-Ray CT). The results show that the larger fraction size is found to have less spheres and rods, and more discs than the smaller one, and there is a significant difference in grain size obtained by 3D analysis and sieve analysis. The difference becomes greater in the larger fraction size, and 3D analysis gives smaller values of particle size than sieve analysis. This proves that particle shape is a very important factor influencing the grain size distribution of calcareous sand.