Bar (unit)

The bar is a metric unit of pressure, but is not approved as part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa, which is slightly less than the current average atmospheric pressure on Earth at sea level.≡ 106 dyn/cm2≈ 1 mmHg The bar is a metric unit of pressure, but is not approved as part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa, which is slightly less than the current average atmospheric pressure on Earth at sea level. The bar and the millibar were introduced by the Norwegian meteorologist Vilhelm Bjerknes, who was a founder of the modern practice of weather forecasting. The International Bureau of Weights and Measures (BIPM) lists the bar as one of the 'non-SI units should have the freedom to use', but has declined to include it among the 'Non-SI units accepted for use with the SI'. 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 or mb). The notation bar(g), though deprecated by various bodies, represents gauge pressure, i.e., pressure in bars above ambient or atmospheric pressure. The bar is defined using the SI derived unit, pascal: 1 bar ≡ 100,000 Pa ≡ 100,000 N/m2. Thus, 1 bar is equal to: