Standard sea-level pressure, by definition, equals 760 mm (29.92 inches) of mercury, 14.70 pounds per square inch, 1,013.25 × 10 3 dynes per square centimetre, 1,013.25 millibars, one standard atmosphere, or 101.325 kilopascals. It corresponds to the pressure exerted by a vertical column of mercury (as in a barometer) 760 mm (29.9213 inches) high. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Torr and mm-Hg, 0°C are often taken to be identical. In addition (the CGPM noted) there had been some misapprehension that it "led some physicists to believe that this definition of the standard atmosphere was valid only for accurate work in thermometry. It was originally defined as the pressure exerted by 760 mm of mercury at 0 °C and standard gravity (gn = 9.80665 m/s2). Our editors will review what you’ve submitted and determine whether to revise the article. Variations about these values are quite small; for example, the highest and lowest sea-level pressures ever recorded are 32.01 inches (in the middle of Siberia) and … The atmosphere (atm; approximately 1.034 kilograms per square centimetre [14.7 pounds per square inch], equivalent to the weight of about 760 millimetres [30 inches] of mercury) and the bar (equivalent to one kilogram per square centimetre) are often cited. The static pressure at a point in the medium is the pressure that would exist at that point with no sound waves present. , "Electricity and Gas Inspection Act", SOR/86-131 (defines a set of standard conditions for Imperial units and a different set for metric units), "Standards of Performance for New Sources", 40 CFR—Protection of the Environment, Chapter I, Part 60, Section 60.2, 1990, "National Primary and Secondary Ambient Air Quality Standards", 40 CFR—Protection of the Environment, Chapter I, Part 50, Section 50.3, 1998, "Storage and Handling of Liquefied Petroleum Gases" and "Storage and Handling of Anhydrous Ammonia", 29 CFR—Labor, Chapter XVII—Occupational Safety and Health Administration, Part 1910, Sect. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. See also millibar. Let us know if you have suggestions to improve this article (requires login). This is a pressure of 101 325 Pa.  This defined both temperature and pressure independent of the properties of particular substance. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101325 Pa (1.01325 bar). ", In chemistry and in various industries, the reference pressure referred to in "standard temperature and pressure" (STP) was commonly 1 atm (101.325 kPa) but standards have since diverged; in 1982, the International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the physical properties of substances, "standard pressure" should be precisely 100 kPa (1 bar).. 1910.110 and 1910.111, 1993, "Rule 102, Definition of Terms (Standard Conditions)", Amended December 2004, South Coast Air Quality Management District, Los Angeles, California, USA, ANSI/AMCA Standard 210, "Laboratory Methods Of Testing Fans for Aerodynamic Performance Rating", as implied by, International Union of Pure and Applied Chemistry, National Institute of Standards and Technology, Modern Thermodynamics with Statistical Mechanics, International Organization for Standardization, United States Environmental Protection Agency, American Association of Physicists in Medicine, "20 °C – A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements", "Status of the Nord Stream pipeline route in the Baltic Sea", "Natural gas purchase and sale agreement", "NIST Standard Reference Database 124 – Stopping-Power and Range Tables for Electrons, Protons, and Helium Ions", "ISO 10780:1994 : Stationary source emissions – Measurement of velocity and volume flowrate of gas streams in ducts", "Design and Uncertainty for a PVTt Gas Flow Standard", "What is the difference between STP and NTP?  For example, underwater pressure of 3 ata would mean that pressure includes 1 atm of air above water and also 2 atm of water itself. Standard atmosphere, unit of pressure, equal to the mean atmospheric pressure at sea level. Coincidently, these units are almost identical (1…, …per square centimetre, millibars (mb), standard atmospheres, or kilopascals. One standard atmosphere, which is also referred to as one atmosphere, is equivalent to 101,325 pascals, or newtons of force per square metre (approximately 14.7 pounds per square inch). In 1954, the 10th General Conference on Weights and Measures (CGPM) adopted standard atmosphere for general use and affirmed its definition of being precisely equal to 1013250 dynes per square centimetre (101325 Pa). It corresponds to the pressure exerted by a vertical column of mercury (as in a barometer) 760 mm (29.9213 inches) high. A pressure of 1 atm can also be stated as: The ata unit is used in place of atm to indicate the total pressure of the system, compared to the pressure of the medium vs vacuum only.  It was used as a reference condition for physical and chemical properties, and was implicit in the definition of the centigrade (later Celsius) scale of temperature by defining 100 °C as being the boiling point of water at this pressure. At normal barometric pressure, P 0 equals approximately 10 5 Pa. Standard atmospheric pressure is usually taken to be 0.760 m Hg at 0°C. Updates? This article was most recently revised and updated by, https://www.britannica.com/science/standard-atmosphere-unit-of-measurement. The standard atmosphere (symbol: atm) is a unit of pressure defined as 101325 Pa (1.01325 bar). It is approximately equal to Earth's atmospheric pressure at sea level. It is approximately equal to Earth's atmospheric pressure at sea level. The new value is the mean atmospheric pressure at an altitude of about 112 metres, which is closer to the worldwide median altitude of human habitation (194 m). [ citation needed ] Natural gas companies in Europe, Australia, and South America have adopted 15 °C (59 °F) and 101.325 kPa (14.696 psi) as their standard gas volume reference conditions, used as the base values for defining the standard cubic … Announcing our NEW encyclopedia for Kids! Omissions? It is sometimes used as a reference or standard pressure. It is sometimes used as a reference or standard pressure. Corrections? ", "AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams", "The SI Metric System of Units and SPE Metric Standard (1982)", "Chapter 3 – Effects of Altitude and Atmospheric Conditions (Exterior Ballistics Section)", http://www.greenheck.com/pdf/centrifugal/Plug.pdf, "Fundamental Physical Properties: Molar Volumes (CODATA values for ideal gases)", https://en.wikipedia.org/w/index.php?title=Standard_conditions_for_temperature_and_pressure&oldid=984951465, Articles with dead external links from January 2018, Articles with permanently dead external links, Articles with dead external links from February 2017, Articles with unsourced statements from April 2010, Articles with unsourced statements from May 2012, Creative Commons Attribution-ShareAlike License, EGIA: Electricity and Gas Inspection Act (of Canada), SATP: Standard Ambient Temperature and Pressure, This page was last edited on 23 October 2020, at 02:15. This is the customarily accepted value for cm–H. General Conference on Weights and Measures, International Union of Pure and Applied Chemistry, Standard conditions for temperature and pressure, https://en.wikipedia.org/w/index.php?title=Standard_atmosphere_(unit)&oldid=975148336, Creative Commons Attribution-ShareAlike License, This page was last edited on 27 August 2020, at 00:29. Standard sea-level pressure, by definition, equals 760 mm (29.92 inches) of mercury, 14.70 pounds per square inch, 1,013.25 × 10. See also millibar. For most practical purposes (to 5 significant digits), they are interchangeable. K) as the value of R. However, the USSA,1976 does recognize that this value is not consistent with the values of the Avogadro constant and the Boltzmann constant. One standard atmosphere, which is also referred to as one atmosphere, is equivalent to 101,325 pascals, or newtons of force per square metre (approximately 14.7 pounds per square inch).
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