Abstract: The mechanical behaviors of sand are heavily dependent on its relative density: the dense sand exhibits softening strength; on the contrary, the loose one displays hardening strength. Furthermore, the relative density is determined based on the maximum and minimum void ratios. The maximum and minimum void ratios are commonly obtained by using the maximum and minimum densities, ignoring the effects of test methods and clay contents in sand. The maximum and minimum void ratios are tested by considering three different sized groups of sands with various clay contents. It is shown that the minimum dry density can be attained in a measuring cylinder with low rotation speed. In addition, it is suggested that the maximum dry density of fine sands should be measured with the 250 mL compaction cylinder combining vibration with hit, while the 1000 mL compaction cylinder is suitable for medium and coarse sands. The results also show that the void ratio decreases with the increase in clay contents (less than 30%), while there is a linear relationship between the clay contents and the void ratio of sands. However, the maximum void ratio of sand decreases with increasing content of silty clay and clay, and increases with increasing content of kaolin clay.