Abstract Present paper focuses on the modeling of size effect on the compressive strength of normal strength concrete with the application of discrete element method, considering specimen of different concrete mixes and shapes. An equation was derived to estimate the parallel bond strength from the compressive strength. The results showed a good agreement with the literature and the derived estimation models showed strong correlation with the measurements. The results indicated that size effect is stronger on concretes with lower strength class and that it is more significant on cube specimens than on cylinders. The relationship of model size and computational time was analyzed and a method to decrease the computational time (iterations) was proposed.