Abstract: A statistic of 3926 diamond jewelry indicates that about 97% of the diamonds in China market are standard round, the carats of the most diamonds are no more than 0.42 ct and the ratio of weight of diamond to ring is less than 3.2%. The statistics also show a good linear relation between the weight of diamonds and rings. According to these statistical results and the estimate formulas of the weight and volume of standard round diamond developed before, it is certified that the hydrostatic mechanics method is feasible in non-disassembled measuring the weight and quality (density) of the metal of standard round diamond jewelry. The developed formulas show that the error for estimating the weight of metal is less than 0.01 gram whilc for density, no more than 1.2%. The measuring steps are recommended in this paper. It is affirmed that such method also is acceptable for other gems in a same shape as standard round diamond.