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The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (g n = 9.806 65 m/s 2). [2] It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure.
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2]
at each geopotential altitude, where g is the standard acceleration of gravity, and R specific is the specific gas constant for dry air (287.0528J⋅kg −1 ⋅K −1). The solution is given by the barometric formula. Air density must be calculated in order to solve for the pressure, and is used in calculating dynamic pressure for moving vehicles.
Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa), which is equal to one millibar, and the kilopascal (1 kPa = 1000 Pa), which is equal to one centibar. The unit of measurement called standard atmosphere (atm) is defined as 101,325 Pa . [ 2 ]
Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 bar (100 kPa, 10 5 Pa). NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). [3] This standard is also called normal temperature and pressure (abbreviated as NTP).
The US Navy Diving Manual gives conversion factors for "fw" (feet water) based on a fresh water density of 62.4 lb/ft 3 and for fsw based on a sea water density of 64.0 lb/ft 3. [1] One standard metre sea water equals: [1] 3.263 36 fsw; 102.018 cmH 2 O at 15 °C; 0.1 bar by definition; 10.0 kPa, in SI units; 100 000 Ba, in cgs units
The CGS unit of pressure is the barye (Ba), equal to 1 dyn·cm −2, or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre ("g/cm 2" or "kg/cm 2") and the like without properly identifying the force units. But using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as units ...
0 atm Surface of Mars, average 0.006 atm [2] Top of Mount Everest – 8,849 m (29,032 ft) 0.333 atm [3] Pressurized passenger aircraft cabin altitude 8,000 ft (2,400 m) 0.76 atm [4] Sea level atmospheric pressure: 1 atm Surface of Titan: 1.45 atm 10 m depth in seawater: 2 atm 20 m depth in seawater 3 atm Recreational diving depth limit (40 m ...