Standard temperature and pressure

{{Short description|Reference values for temperature and pressure}} {{Distinguish|Standard sea-level conditions}} {{for|the conditions used in thermodynamic evaluations|Standard state}} '''Standard temperature and pressure''' ('''STP'''), or '''standard conditions for temperature and pressure''', are various standard sets of conditions for experimental measurements used to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted. Other organizations have established a variety of other definitions.

In industry and commerce, the standard conditions for temperature and pressure are often necessary for expressing the volumes of gases and liquids and related quantities such as the rate of volumetric flow (the volumes of gases vary significantly with temperature and pressure): standard cubic meters per second (Sm3/s), and normal cubic meters per second (Nm3/s).

Many technical publications (books, journals, advertisements for equipment and machinery) simply state "standard conditions" without specifying them, often substituting the term with older "normal conditions", or "NC". In special cases this can lead to confusion and errors. Good practice always incorporates the reference conditions of temperature and pressure. If not stated, some room environment conditions are supposed, close to 1 atm pressure, {{convert|25|C|F|2}}, and 0% humidity.

== Definitions ==

=== Main definitions === In chemistry, IUPAC changed its definition of standard temperature and pressure in 1982:<ref name="IUPAC print">{{cite book|title=IUPAC. Compendium of Chemical Terminology|year=1997|publisher=Blackwell Scientific Publications|location=Oxford|isbn=0-632-03583-8|author=A. D. McNaught and A. Wilkinson|editor5-first=Alan|editor5-last=McNaught|editor4-first=Aubrey|editor4-last=Jenkins|editor3-first=Bedřich|editor3-last=Košata|editor2-first=Jiří|editor2-last=Jirát|editor1-first=Miloslav|editor1-last=Nič|edition=2nd|url=https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf#page=62|page=54|doi=10.1351/goldbook|quote=Standard conditions for gases: ... and pressure of 105 pascals. The previous standard absolute pressure of 1 atm (equivalent to 101.325 kPa) was changed to 100 kPa in 1982. IUPAC recommends that the former pressure should be discontinued.}}</ref><ref name="IUPAC web">{{cite book|entry=standard pressure|title=IUPAC. Compendium of Chemical Terminology|year=1997|publisher=Blackwell Scientific Publications|location=Oxford|isbn=978-0-9678550-9-7|entry-url=https://goldbook.iupac.org/terms/view/S05921|author=A. D. McNaught and A. Wilkinson|edition=2nd|doi=10.1351/goldbook.S05921}}</ref> * Until 1982, STP was defined as a temperature of {{convert|273.15|K|C F|2|lk=on}} and an absolute pressure of exactly {{convert|1|atm|kPa|3|lk=on|abbr=on}}. * Since 1982, STP has been defined as a temperature of {{convert|273.15|K|C F|2}} and an absolute pressure of exactly {{convert|1|bar|Pa|3|lk=in|abbr=on}}. IUPAC also defines SATP (Standard Ambient Temperature and Pressure) as a temperature of {{convert|298.15|K|C F|2|lk=on}} and an absolute pressure of exactly {{convert|1|atm|kPa|3|abbr=on}}.<ref name="CRC" />

NIST uses a temperature of {{convert|20|C|K F|2}} and an absolute pressure of {{convert|1|atm|kPa|3|abbr=on}}.<ref>{{cite journal|title=20 Degrees Celsius--A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements|journal=NIST |date=January 2007 |volume=112 |issue=1 |pages=1–23 |url=https://www.nist.gov/publications/20-degrees-celsius-short-history-standard-reference-temperature-industrial-dimensional|last1=Doiron |first1=Theodore D. |doi=10.6028/jres.112.001 |pmid=27110451 |pmc=4654601 }}</ref> This standard is also called '''normal temperature and pressure''' (abbreviated as '''NTP'''). However, a common temperature and pressure in use by NIST for thermodynamic experiments is {{convert|298.15|K|C F|2}} and {{convert|1|bar|kPa|3|abbr=on}}.<ref>{{Cite book|last=Helrich|first=Carl S.|url=https://books.google.com/books?id=oU5DICYlDEAC&q=Modern+Thermodynamics+with+Statistical+Mechanics&pg=PA1|title=Modern Thermodynamics with Statistical Mechanics|date=2008-11-14|publisher=Springer Science & Business Media|isbn=978-3-540-85418-0|language=en}}</ref><ref>{{Cite web|title=A Guide to the NIST Chemistry WebBook|url=https://webbook.nist.gov/chemistry/guide/index.html.en-us.en|access-date=2020-10-06|website=webbook.nist.gov}}</ref> NIST also uses {{convert|15|C|K F|2}} for the temperature compensation of refined petroleum products, despite noting that these two values are not exactly consistent with each other.<ref>{{cite web|title=Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices|url=https://www.nist.gov/system/files/documents/2021/05/05/00-20-hb44-web-final_0.pdf|page = 3-1}}</ref>

The '''ISO 13443''' standard reference conditions for natural gas and similar fluids are {{convert|288.15|K|C F}} and {{convert|1|atm|kPa|3|abbr=on}};<ref name="ISO13443" /> by contrast, the American Petroleum Institute adopts {{convert|60|F|C K|2}}.<ref>[https://www.api.org/-/media/files/publications/2022-catalog/petroleum-measurement-2022.pdf API Petroleum Measurement]</ref>

=== Past uses === Before 1918, many professionals and scientists using the metric system of units defined the standard reference conditions of temperature and pressure for expressing gas volumes as being {{convert|15|C|K F|2|lk=on}} and {{convert|101.325|kPa|atm Torr|lk=on|abbr=on|sigfig=3}}. During those same years, the most commonly used standard reference conditions for people using the imperial or U.S. customary systems was {{convert|60|F|C K|2}} and {{convert|14.696|psi|atm|2|abbr=on|sigfig=3}} because it was almost universally used by the oil and gas industries worldwide. The above definitions are no longer the most commonly used in either system of units.<ref>{{cite journal|title=20 °C – A Short History of the Standard Reference Temperature for Industrial Dimensional Measurements|last=Doiron|first=Ted|date=Jan–Feb 2007|journal=Journal of Research of the National Institute of Standards and Technology|volume=112|issue=1|pages=1–23|doi=10.6028/jres.112.001|pmid=27110451|pmc=4654601}}</ref>

=== Current use ===

Many different definitions of standard reference conditions are currently being used by organizations all over the world. The table below lists a few of them, but there are more. Some of these organizations used other standards in the past. For example, IUPAC's new value<ref name="IUPAC web" /> 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),<ref>{{cite journal|title=Hypsographic demography: The distribution of human population by altitude|last1=Cohen|first1=Joel E.|last2=Small|first2=Christopher|date=November 24, 1998|journal=Proceedings of the National Academy of Sciences|volume=95|issue=24|pages=14009–14014|doi=10.1073/pnas.95.24.14009|pmid=9826643|pmc=24316|bibcode=1998PNAS...9514009C |doi-access=free}}</ref> and follows the metric system (Pascal is a metric unit, while atmosphere is not).

Natural gas companies in Europe, Australia, and South America have adopted {{convert|15|C|K F|2|lk=on}} and {{convert|1|atm|kPa|3|lk=on|abbr=on}} as their standard gas volume reference conditions, used as the base values for defining the standard cubic meter.<ref>{{cite web|url=http://www.gassco.no/sw3138.asp |title=Concepts – Standard cubic meter (scm) |access-date=2008-07-25 |author=Gassco |quote=Scm: The usual abbreviation for standard cubic metre – a cubic metre of gas under a standard condition, defined as an atmospheric pressure of 1.01325 bar and a temperature of 15°C. This unit provides a measure for gas volume. |url-status=dead |archive-url=https://web.archive.org/web/20071018212002/http://www.gassco.no/sw3138.asp |archive-date=October 18, 2007 |author-link=Gassco }}</ref><ref>{{cite web |url=http://www.nord-stream.com/uploads/media/Nord_Stream_Route_Status_ENGLISH.pdf |archive-url=https://web.archive.org/web/20080216043432/http://www.nord-stream.com/uploads/media/Nord_Stream_Route_Status_ENGLISH.pdf |url-status=dead |archive-date=2008-02-16 |title=Status of the Nord Stream pipeline route in the Baltic Sea |access-date=2008-07-25 |author=Nord Stream |date=October 2007 |quote=bcm: Billion Cubic Meter (standard cubic metre – a cubic metre of gas under a standard condition, defined as an atmospheric pressure of 1 atm and a temperature of 15 °C.)|author-link=Nord Stream }}</ref><ref>{{cite web |url=http://www.secinfo.com/dsD7y.1a.7.htm |title=Natural gas purchase and sale agreement |access-date=2008-07-25 |author=Metrogas |date=June 2004 |quote=Natural gas at standard condition shall mean the quantity of natural gas, which at a temperature of fifteen (15) Celsius degrees and a pressure of 101.325 kilopascals occupies the volume of one (1) cubic meter.|author-link=Metrogas }}</ref> Also, the International Organization for Standardization (ISO), the United States Environmental Protection Agency (EPA) and National Institute of Standards and Technology (NIST) each have more than one definition of standard reference conditions in their various standards and regulations.

===Comparison table===  {| class="wikitable sortable" style="white-space:nowrap" |+ Standard reference conditions in current use ! colspan=2| Temperature ! colspan=4| Pressure ! Humidity ! rowspan=3 class="unsortable" | Publishing or establishing entity |- ! °C ! °F ! kPa ! mmHg ! psi ! inHg ! % |- ! !! !! !! !! !! !!   |- |{{convert|0|C|F|disp=tablecen|sortable=on}}||{{convert|100.000|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | || International Union of Pure and Applied Chemistry |IUPAC (STP) since 1982<ref name="IUPAC print" /> |- |{{convert|0|C|F|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | ||NIST,<ref name="NISTDataBase7">{{cite web|url=https://www.nist.gov/pml/data/star/index.cfm |title=NIST Standard Reference Database 124 – Stopping-Power and Range Tables for Electrons, Protons, and Helium Ions |access-date=2008-07-25 |author=NIST |year=1989 |quote=If you want the program to treat the material as an ideal gas, the density will be assumed given by ''M''/''V'', where ''M'' is the gram molecular weight of the gas and ''V'' is the mol volume of 22414 cm3 at standard conditions (0 deg C and 1 atm). |url-status=dead |archive-url=https://web.archive.org/web/20101006154629/https://www.nist.gov/pml/data/star/index.cfm |archive-date=October 6, 2010 |author-link=National Institute of Standards and Technology }}</ref> ISO 10780,<ref name="ISO10780">{{cite web |author=ISO | title=ISO 10780:1994 : Stationary source emissions – Measurement of velocity and volume flowrate of gas streams in ducts |year=1994 |url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=18855| author-link=International Organization for Standardization }}</ref> formerly IUPAC (STP) until 1982<ref name="IUPAC print" />

|- |{{convert|15|C|F|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | style="text-align:center;" |0 ||ICAO's ISA,<ref name="Handbook"> {{cite book|editor=Robert C. Weast |title=Handbook of Physics and Chemistry|edition=56th|publisher=CRC Press|pages=F201–F206|year=1975|isbn=978-0-87819-455-1}}</ref> ISO 13443,<ref name="ISO13443">{{cite book |title=Natural gas – Standard reference conditions (ISO 13443) |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=20461 |year=1996}}</ref> EEA,<ref name="EEA">{{cite book |title=Extraction, First Treatment and Loading of Liquid & Gaseous Fossil Fuels (Emission Inventory Guidebook B521, Activities 050201 – 050303) |date=September 1999 |publisher=European Environmental Agency |location=Copenhagen, Denmark |url=https://www.eea.europa.eu/publications/EMEPCORINAIR3/B521vs3.1.pdf/view |format=PDF }}</ref> EGIA{{Efn|Electricity and Gas Inspection Act (of Canada).|name=test}} (SI Definition)<ref name="EGIA">{{Cite web|title=Electricity and Gas Inspection Regulations|url=http://laws.justice.gc.ca/en/E-4/SOR-86-131/95708.html|website=laws.justice.gc.ca|access-date=2026-01-29|archive-url=https://web.archive.org/web/20050103235031/http://laws.justice.gc.ca/en/E-4/SOR-86-131/95708.html|archive-date=2005-01-03|last=Government of Canada, Department of Justice}}</ref>, [https://www.thermexcel.com/french/tables/massair.htm Air density 1.225 kg/m³]

|- |{{convert|20|C|F|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | ||EPA,<ref name="NSPS">"Standards of Performance for New Sources", 40 CFR—Protection of the Environment, Chapter I, Part 60, Section 60.2, 1990.</ref> NIST.<ref name="NISTJournal">{{cite journal |title=Design and Uncertainty for a PVTt Gas Flow Standard |journal=Journal of Research of the National Institute of Standards and Technology |volume=108 |year=2003 |url=http://www.cstl.nist.gov/div836/836.01/PDFs/2003/j80wri.pdf |archive-url=https://web.archive.org/web/20040721040809/http://www.cstl.nist.gov/div836/836.01/PDFs/2003/j80wri.pdf |url-status=dead |archive-date=2004-07-21 |issue=1 |pages=21–47 |doi=10.6028/jres.108.004 |pmid=27413592 |pmc=4844527 |last1=Wright |first1=J. D. |last2=Johnson |first2=A. N. |last3=Moldover |first3=M. R. }}</ref><ref>(Also called NTP, Normal Temperature and Pressure.)</ref><ref>{{Cite web |url=http://socratic.org/questions/what-is-the-difference-between-stp-and-ntp |title=What is the difference between STP and NTP?|website=Socratic |access-date=2018-08-28 |archive-url=https://web.archive.org/web/20151127035351/http://socratic.org/questions/what-is-the-difference-between-stp-and-ntp |archive-date=2015-11-27 |url-status=dead }}</ref>

|- |{{convert|22|C|F|1|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | style="text-align:center;" |{{val|20|-|80}}||American Association of Physicists in Medicine<ref name="MedPHys">{{cite journal |title=AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams|journal=Medical Physics |volume=26 |year=1999|issue=9|pages=1847–1870 |doi=10.1118/1.598691|pmid=10505874 |bibcode=1999MedPh..26.1847A|last1=Almond |first1=Peter R. |last2=Biggs |first2=Peter J. |last3=Coursey |first3=B. M. |last4=Hanson |first4=W. F. |last5=Huq |first5=M. Saiful |last6=Nath |first6=Ravinder |last7=Rogers |first7=D. W. O. |s2cid=12687636 |doi-access=free }}</ref>

|- |{{convert|25|C|F|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | ||   |IUPAC (SATP),<ref name="CRC">"CRC Handbook of Chemistry and Physics", Definition of Ambient, Chapter 1-26, 95th Edition, William M. Haynes, ed., CRC Press, Boca Raton, FL, 2014.</ref> EPA<ref name="NAAQS">"National Primary and Secondary Ambient Air Quality Standards", 40 CFR—Protection of the Environment, Chapter I, Part 50, Section 50.3, 1998.</ref>

|- |{{convert|20|C|F|disp=tablecen|sortable=on}}||{{convert|100.000|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | style="text-align:center;" |0||CAGI<ref name="CAGI">{{cite web |title=Glossary |year=2002 |publisher=Compressed Air and Gas Institute |location=Cleveland, OH, US |url=http://www.cagi.org/toolbox/glossary.htm |archive-url=https://web.archive.org/web/20070902020158/http://www.cagi.org/toolbox/glossary.htm |url-status=dead |archive-date=2007-09-02}}</ref>

|- |{{convert|15|C|F|disp=tablecen|sortable=on}}||{{convert|100.000|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | ||   |SPE<ref name="SPE">{{cite web |url=https://www.spe.org/authors/docs/metric_standard.pdf |title=The SI Metric System of Units and SPE Metric Standard (1982) |at=Standard Temperature (Page 24), and Notes for Table 2.3, (on PDF page 25 of 42 PDF pages), define two different sets of reference conditions, one for the standard cubic foot and one for the standard cubic meter |publisher=Society of Petroleum Engineers}}</ref>

|- |{{convert|20|C|F|disp=tablecen|sortable=on}}||{{convert|101.3|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | style="text-align:center;" |50|| ISO 5011<ref name="ISO5011">{{cite book |title=Air Intake Filters (ISO 5011:2002) |year=2002 |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=http://www.iso.org/iso/en/prods-services/ISOstore/store.html}}</ref>

|- |{{convert|20|C|F|disp=tablecen|sortable=on}}||{{convert|760.0|mmHg|kPa|disp=tablecen|sortable=on|order=flip}} | style="text-align:center;" |{{convert|760.0|mmHg|psi|disp=number|sortable=on}}|| style="text-align:center;" |{{convert|760.0|mmHg|inHg|disp=number|sortable=on}} | style="text-align:center;" |0||GOST 2939-63

|- |{{convert|60|F|C|2|disp=tablecen|sortable=on|order=flip}}||{{convert|14.696|psi|kPa mmHg|disp=tablecen|sortable=on|order=flip}} | style="text-align:center;" |{{convert|14.696|psi|inHg|disp=number|sortable=on}} | ||SPE,<ref name="SPE" /> U.S. OSHA,<ref name="OSHA">"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. 1910.110 and 1910.111, 1993  [https://web.archive.org/web/20060719085519/http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=f169acd0f57a17565c9984fa0f57d285&rgn=div8&view=text&node=29%3A5.1.1.1.8.8.33.10&idno=29 Storage/Handling of LPG].</ref> SCAQMD<ref name="SCAQMD">"Rule 102, Definition of Terms (Standard Conditions)", Amended December 2004, South Coast Air Quality Management District, Los Angeles, California, US  [http://www.aqmd.gov/ SCAQMD Rule 102]</ref>

|- |{{convert|60|F|C|2|disp=tablecen|sortable=on|order=flip}}||{{convert|14.73|psi|kPa mmHg|disp=tablecen|sortable=on|order=flip}} | style="text-align:center;" |{{convert|14.73|psi|inHg|disp=number|sortable=on}} | ||EGIA{{Efn|Electricity and Gas Inspection Act (of Canada).|name=test}} (Imperial System Definition)<ref name="EGIA" />

|- |{{convert|60|F|C|2|disp=tablecen|sortable=on|order=flip}}||{{convert|14.7|psi|kPa mmHg|2|disp=tablecen|sortable=on|order=flip}} | style="text-align:center;" |{{convert|14.7|psi|inHg|2|disp=number|sortable=on}} | ||   |U.S. DOT (SCF)<ref name="USDOT">{{cite web|url=https://www.ecfr.gov/cgi-bin/text-idx?SID=4cb9c4fbd569caade0b61e28dec528f2&mc=true&node=se49.2.171_18&rgn=div8 |title=49 C.F.R. § 171 |access-date=22 May 2018}}</ref>

|- |{{convert|59|F|C|disp=tablecen|sortable=on|order=flip}}||{{convert|14.503|psi|kPa mmHg|disp=tablecen|sortable=on|order=flip}} | style="text-align:center;" |{{convert|14.503|psi|inHg|disp=number|sortable=on}} | style="text-align:center;" |78|||U.S. Army Standard Metro<ref name="ArmyStdMetro">{{cite book |chapter-url=http://www.exteriorballistics.com/ebexplained/5th/31.cfm |title=Rifle and Handgun Reloading Manual |edition=5 |chapter=Chapter 3 – Effects of Altitude and Atmospheric Conditions (Exterior Ballistics Section) |author=Sierra Bullets |location=Sedalia, MO, US |access-date=2006-02-03 |archive-date=2006-03-09 |archive-url=https://web.archive.org/web/20060309023230/http://www.exteriorballistics.com/ebexplained/5th/31.cfm |url-status=dead }}</ref>{{efn|The pressure is specified as 750 mmHg. However, the mmHg is temperature-dependent, since mercury expands as temperature goes up. Here the values for the 0–20 °C range are given.}}

|- |{{convert|59|F|C|disp=tablecen|sortable=on|order=flip}}||{{convert|14.696|psi|kPa mmHg|disp=tablecen|sortable=on|order=flip}} | style="text-align:center;" |{{convert|14.696|psi|inHg|disp=number|sortable=on}} | style="text-align:center;" |60||ISO 2314,<ref name="ISO2314">{{cite book |title=Gas turbines – Acceptance tests (ISO 2314:2009) |year=2009 |edition=2 |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=https://www.iso.org/standard/42989.html}}</ref> ISO 3977-2,<ref name="ISO3977-2">{{cite book |title=Gas turbines – Procurement – Part 2: Standard reference conditions and ratings (ISO 3977-2:1997) |year=1997 |publisher=International Organization for Standardization |location=Geneva, Switzerland |url=https://www.iso.org/standard/24755.html}}</ref> ASHRAE Fundamentals Handbook<ref>{{Cite web |title=ASHRAE Handbook Online |url=https://www.ashrae.org/technical-resources/ashrae-handbook/ashrae-handbook-online |access-date=2023-08-09 |website=www.ashrae.org}}</ref>

|- |{{convert|70|F|C|2|disp=tablecen|sortable=on|order=flip}}||{{convert|29.92|inHg|kPa mmHg psi|disp=tablecen|sortable=on|order=flip}} | style="text-align:center;" |0||AMCA,<ref name="AMCA">ANSI/AMCA Standard 210, "Laboratory Methods Of Testing Fans for Aerodynamic Performance Rating", as implied by http://www.greenheck.com/pdf/centrifugal/Plug.pdf when accessed on October 17, 2007.</ref>{{efn|The standard is given as 29.92 inHg at an unspecified temperature. This most likely corresponds to a standard pressure of 101.325 kPa, converted into ~29.921 inHg at {{convert|32|F|C}}.}} air density = 0.075 lbm/ft3.<ref>This AMCA standard applies only to air; Compressed Gas Association [CGA] applies to industrial gas use in US.</ref><ref>{{cite book|title=Compressed Gas Handbook|url=https://books.google.com/books?id=5EfhBwAAQBAJ&q=%22compressed+gas+association%22+handbook+fifth+edition|access-date=22 Nov 2017|isbn = 9781461306733|last1 = Association|first1 = Compressed Gas|date = 2012-12-06| publisher=Springer }}</ref>

|- |{{convert|59|F|C|disp=tablecen|sortable=on|order=flip}}||{{convert|29.92|inHg|kPa mmHg psi|disp=tablecen|sortable=on|order=flip}} | ||FAA<ref name="FAA">{{cite book|year=2016|title=Pilot's Handbook of Aeronautical Knowledge|url=https://www.faa.gov/sites/faa.gov/files/2022-03/pilot_handbook.pdf|publisher=U.S. Department of Transportation Federal Aviation Administration|page=4{{hyphen}}3}}</ref>

|- |{{convert|20|C|F|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | | | 0 | EN 14511-1:2013<ref name="EN14511-1:2013">{{cite book |title=Air Conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling |year=2013 |publisher=BSI EN|location=UK|url=https://shop.bsigroup.com/ProductDetail/?pid=000000000030271396}}</ref>

|- |{{convert|15|C|F|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | style="text-align:center;" |0||ISO 2533:1975<ref name="ISO2533:1975">{{cite book |title=Standard Atmosphere|year=1975|publisher=International Organization for Standardization|location=Geneva, Switzerland|url=https://www.iso.org/standard/7472.html}}</ref> ISO 13443:2005,<ref name="ISO13443:1996">{{cite book |title=Natural gas - Standard reference conditions|year=1996|publisher=International Organization for Standardization|location=Geneva, Switzerland|url=https://www.iso.org/standard/20461.html}}</ref> ISO 7504:2015<ref name="ISO7504:2015">{{cite book |title=Gas analysis - Vocabulary|year=2015|publisher=International Organization for Standardization|location=Geneva, Switzerland|url=https://www.iso.org/standard/53596.html}}</ref>

|- |{{convert|0|C|F|disp=tablecen|sortable=on}}||{{convert|101.325|kPa|mmHg psi inHg|disp=tablecen|sortable=on}} | style="text-align:center;" |0||DIN 1343:1990<ref name="DIN1343:1990">{{cite book |title=Referenzzustand, Normzustand, Normvolumen; Begriffe und Werte|year=1990|publisher=Deutsches Institut für Normung|location=Germany|url=https://www.din.de/en/getting-involved/standards-committees/natg/standards/wdc-beuth:din21:1505240 }}</ref> |}

==International Standard Atmosphere== In aeronautics and fluid dynamics the "International Standard Atmosphere" (ISA) is a specification of pressure, temperature, density, and speed of sound at each altitude. At standard mean sea level it specifies a temperature of {{convert|15|C|F}}, pressure of {{convert|101325|Pa|psi}} (1 atm), and a density of {{convert|1.2250|kg/m3|lb/ft3|sp=us}}. It also specifies a temperature lapse rate of −6.5 °C (−11.7 °F) per km (approximately −2 °C (−3.6 °F) per 1,000 ft).<ref name="aeromech.usyd.edu.au">{{Cite web | last1 = Auld | first1 = D.J. | last2 = Srinivas | first2 = K. | title = Properties of the Atmosphere | date = 2008 | url = http://www.aeromech.usyd.edu.au/aero/atmosphere/ | access-date = 2008-03-13 | archive-url = https://web.archive.org/web/20130609091708/http://www.aeromech.usyd.edu.au/aero/atmosphere/ | archive-date = 2013-06-09 | url-status = dead }}</ref><ref name="Batchelor 1967">Batchelor, G. K., ''An Introduction to Fluid Dynamics'', Cambridge Univ. Press, 1967.</ref>

The International Standard Atmosphere is representative of atmospheric conditions at mid latitudes. In the US this information is specified the U.S. Standard Atmosphere which is identical to the "International Standard Atmosphere" at all altitudes up to 65,000 feet above sea level.{{citation needed|date=May 2012}}

==Standard laboratory conditions== Because many definitions of standard temperature and pressure differ in temperature significantly from standard laboratory temperatures (e.g. 0 °C vs. ~28 °C), reference is often made to "standard laboratory conditions" (a term deliberately chosen to be different from the term "standard conditions for temperature and pressure", despite its semantic near identity when interpreted literally). However, what is a "standard" laboratory temperature and pressure is inevitably geography-bound, given that different parts of the world differ in climate, altitude and the degree of use of heat/cooling in the workplace. For example, schools in New South Wales, Australia use 25 °C at 100 kPa for standard laboratory conditions.<ref>{{cite book|author=Peter Gribbon|title=Excel HSC Chemistry Pocket Book Years 11–12|publisher=Pascal Press|year=2001|isbn=978-1-74020-303-6}}</ref> ASTM International has published Standard ASTM E41- Terminology Relating to Conditioning and hundreds of special conditions for particular materials and test methods. Other standards organizations also have specialized standard test conditions.{{cn|date=May 2023}}

==Molar volume of a gas== {{see also|Standard cubic feet|Oil barrel}}

It is as important to indicate the applicable reference conditions of temperature and pressure when stating the molar volume of a gas<ref>{{cite web |url=http://physics.nist.gov/cgi-bin/cuu/Results?search_for=volume+molar |title=Fundamental Physical Properties: Molar Volumes (CODATA values for ideal gases) |publisher=NIST}}</ref> as it is when expressing a gas volume or volumetric flow rate. Stating the molar volume of a gas without indicating the reference conditions of temperature and pressure has very little meaning and can cause confusion.

The molar volume of gases around STP and at atmospheric pressure can be calculated with an accuracy that is usually sufficient by using the ideal gas law. The molar volume of any ideal gas may be calculated at various standard reference conditions as shown below: * ''V''m = 8.3145 × 273.15 / 101.325 = 22.414 dm3/mol at 0 °C and 101.325 kPa * ''V''m = 8.3145 × 273.15 / 100.000 = 22.711 dm3/mol at 0 °C and 100 kPa * ''V''m = 8.3145 × 288.15 / 101.325 = 23.645 dm3/mol at 15 °C and 101.325 kPa * ''V''m = 8.3145 × 298.15 / 101.325 = 24.466 dm3/mol at 25 °C and 101.325 kPa * ''V''m = 8.3145 × 298.15 / 100.000 = 24.790 dm3/mol at 25 °C and 100 kPa * ''V''m = 10.7316 × 519.67 / 14.696 = 379.48 ft3/lbmol at 60 °F and 14.696 psi (or about 0.8366 ft3/gram mole) * ''V''m = 10.7316 × 519.67 / 14.730 = 378.61 ft3/lbmol at 60 °F and 14.73 psi

Technical literature can be confusing because many authors fail to explain whether they are using the ideal gas constant ''R'', or the specific gas constant ''R''s. The relationship between the two constants is ''R''s = ''R'' / ''m'', where ''m'' is the molecular mass of the gas.

The US Standard Atmosphere (USSA) uses 8.31432 m3·Pa/(mol·K) as the value of ''R''. However, the USSA in 1976 does recognize that this value is not consistent with the values of the Avogadro constant and the Boltzmann constant.<ref name="USSA1976">[https://www.ngdc.noaa.gov/stp/space-weather/online-publications/miscellaneous/us-standard-atmosphere-1976/us-standard-atmosphere_st76-1562_noaa.pdf ''U.S. Standard Atmosphere, 1976''], U.S. Government Printing Office, Washington, D.C., 1976.</ref>

==See also== * Environmental chamber * ISO 1 – standard reference temperature for geometric product specifications * Reference atmospheric model * Room temperature * Standard sea-level conditions * Standard state

== Explanatory notes == {{notelist}}

==References== {{Reflist}}

==External links== * [http://goldbook.iupac.org/S05910.html "Standard conditions for gases"] from the IUPAC ''Gold Book''. * [http://goldbook.iupac.org/S05921.html "Standard pressure"] from the IUPAC ''Gold Book''. * [http://goldbook.iupac.org/S06036.html "STP"] from the IUPAC ''Gold Book''. * [http://goldbook.iupac.org/S05925.html "Standard state"] from the IUPAC ''Gold Book''.

Category:Atmospheric thermodynamics Category:Aerodynamics Category:Engineering thermodynamics Category:Gases Category:Measurement Category:Physical chemistry Category:Standards Category:Thermodynamics