Ill just share this..
In the aviation industry.. everything is based off "standard conditions" .. The ICAO (International Civil Aviation Organization) recognized the ISA (International Standard Atmosphere) which is 59* F at Sea Level with 14.7 psi (1013.25 hPa)and 0% humidity. These standard conditions yield the best results when rating aircraft performance and data interpretation.
In the Army Standard Metro atmosphere, now used only in ballistics, defines sea-level conditions as 29.5275 inHg of pressure (99.9916 kPa), 59°F (15°C), and 78% humidity.
In chemistry, the term standard temperature and pressure (abbreviated STP) denotes an exact reference temperature of 0°C (273.15 K) and pressure of 1 atm (defined as 101.325 kPa). These values approximate freezing temperature of water and atmospheric pressure at sea level. Also in chemistry, the term Standard Ambient Temperature and Pressure (abbreviated SATP) denotes a reference temperature of 25°C (298.15 K) and pressure of 100 kPa. Although there are many variations of the definition, the most accepted one is the temperature and pressure where the equilibrium constant for the autoionization of water is 1.0x10-14.
For practical uses? I would use the ICAO Aviation standard for ideal conditions.