Abstract: The sectional area of round wires of copper alloy were measured by weighing method and calculation method respectively. The standard measurement uncertainty of resistivity used by these two methods of round wires of copper alloy specimens was evaluated by experiments. The results show that sectional area and expanded uncertainty of resistivity measured by weighing method were greater than that measured by calculation method. For round wires whose dimensional deviations meet the standard requirements, the results of resistivity obtained by using calculation method to measure sectional area were more reliable.