Bar (unit)

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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...

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