Bar (unit)
non-SI unit of pressure
The bar (symbol bar) is a metric unit of pressure defined as 100000 Pa (100 kPa or 1000 hPa), though not part of the International System of Units (SI). A pressure of 1 bar is slightly less than the average atmospheric pressure on Earth at sea level (approximately 1.013 bar). By the barometric formula, 1 bar is roughly the atmospheric pressure on Earth at an altitude of 111 metres at 15 °C.
The bar and the millibar (symbol mbar) were introduced by the Norwegian meteorologist Vilhelm Bjerknes, a founder of the modern practice of weather forecasting, with the bar defined as one megadyne per square centimetre.
The SI brochure lists the symbol and value for the bar but it is not an SI unit. The bar has been legally recognised in countries of the European Union since 2004. The US National Institute of Standards and Technology (NIST) deprecates its use except for "limited use in meteorology" and lists it as one of several units that "must not be introduced in fields where they are not presently used". The International Astronomical Union (IAU) also lists it under "Non-SI units and symbols whose continued use is deprecated".
Units derived from the bar include the megabar (symbol: Mbar), kilobar (symbol: kbar), decibar (symbol: dbar), centibar (symbol: cbar), and millibar (symbol: mbar). The microbar (symbol: μbar) is used in acoustics.
Definition and conversion
The bar is defined using the SI derived unit, pascal: 1 bar ≡ 100000 Pa ≡ 100000 N/m2.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Jun 15, 2026. The linked authority identifier is Q103510. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1000 and 2004.
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This entry incorporates text from “Bar (unit)” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.