Mass = density * volume.

Air density is p/RT, where R is the gas constant for air (287 J/kg-K), T is the absolute temperature, and p is the pressure, equal to 101325 Pa at sea level.

At sea level and room temperature, the density of air is

rho 101325 N/m2/ (287 N-m/ (kg-K)*293 K

or about a) 2 kg/mc)