Designing ruble mound structures with stone armour is challenging task due to insecurities in design parameters. That is the reason multiple formulas for the stability and the size of the stone armour exist. This paper analyzes Hudson, Van der Meer and Van Gent formulas for calculating the size of stone armour of rubble mound breakwaters, as well as Vidal formula for calculating the size of stone armour of submerged breakwater. The thesis primarily analyzed if the slope of the seabed influenc the size of the stone armour. Therefore, three typical sections of the coast were chosen, with the calculation being done for typical waves of significant wave heights of 2, 3 and 4 meters. According to Van der Meer formula, the slope of the seabed influenced the size of the stone armour only at the breaking point, which differs depending on the seabed slope, while the change in size of stone armour from the deep point to the breaking point remained identical for all three types of slopes. On the other hand, Hudson formula, when compared to Van der Meer, gave significantly higher values of the size of stone armour due to restricted number of influential parameters, while it regulates breaking point only through stability coefficient. Van Gent formula, which is used in areas of shallow waters, gave similar results to Van der Meer one, considering that it takes into account the wave height at the structure's toe.