Density of air
The density of air (air density) is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variation in temperature or humidity. At sea level and at 15 °C air has a density of approximately 1.225 kg/m3 (0.001225 g/cm3, 0.0023769 slug/(cu ft), 0.0765 lb/(cu ft)) according to ISA (International Standard Atmosphere).
The air density is a property used in many branches of science as aeronautics;gravimetric analysis; the air-conditioning industry; atmospheric research and meteorology; the agricultural engineering in their modeling and tracking of Soil-Vegetation-Atmosphere-Transfer (SVAT) models; and the engineering community that deals with compressed air from industry utility, heating, drying and cooling processes in industries like cooling towers, vacuum and deep vacuum processes, high pressure processes, gas and light oil combustion processes that power turbine-powered airplanes, gas turbine-powered generators and heating furnaces, and air conditioning from deep mines to space capsules.
Depending on the measuring instruments, use, area of expertise and necessary rigor of the result different calculation criteria and sets of equations for the calculation of the density of air are used. This topic are some examples of calculations with the main variables involved, the amounts presented throughout these examples are properly referenced usual values, different values can be found in other references depending on the criteria used for the calculation . Furthermore we must pay attention to the fact that air is a mixture of gases and the calculation always simplify, to a greater or lesser extent, the properties of the mixture and the values for the composition according to the criteria of calculation.
The density of dry air can be calculated using the ideal gas law, expressed as a function of temperature and pressure:
...
Wikipedia