Page "Atmospheric pressure" Paragraph 2

In 1971, the International Union of Pure and Applied Chemistry ( IUPAC ) said that for the purposes of specifying the properties of substances, " the standard pressure " should be defined as precisely 100 kPa (≈ 750. 01 torr ) or 29. 53 inHg rather than the 101. 325 kPa value of “ one standard atmosphere ”.

This value is used as the standard pressure for the compressor and the pneumatic tool industries ( ISO 2787 ).

( See also Standard temperature and pressure.

) In the United States, compressed air flow is often measured in " standard cubic feet " per unit of time, where the " standard " means the equivalent quantity of air at standard temperature and pressure.

For every 1, 000 feet you ascend, the atmospheric pressure decreases by about 4 %.

However, this standard atmosphere is defined slightly differently: temperature =, air density