Mercury, the element, has a density of approximately 13.5 to 13.6 kg/m^3, and its overall mass depends on the volume collected. The planet Mercury has a mass of approximately 3.3 * 10^23 kilograms, or .055 times the mass of the Earth.
According to The Physics Hypertextbook, the element mercury has a density of approximately 13.594 kg/m^3. PeriodicTable.com reports a slightly different density of 13.534 g/cm^3. Given a certain volume of mercury, the mass can be found by multiplying its volume by the density of mercury. For example, the mass of 2 cubic meters of mercury is (2 m^3 * 13.594 kg/m^3) = 27.188 kg. Convert kilograms to pounds by multiplying the number of kilograms by 2.2046.
According to NASA, the planet Mercury has a mass of approximately 3.3010 * 10^23 kg.