Bar (unit)

bar
A pressure of 700 bar flattened this length of aluminium tubing of wall thickness 5 millimetres (0.20 in).
General information
Unit system	Metric system
Unit of	pressure
Symbol	bar
Conversions
1 bar in ...	... is equal to ...
SI units	100 kPa
CGS units	106 Ba
US customary units	14.50377 psi
Atmospheres	0.986923 atm

The bar is a metric unit of pressure defined as 100,000 Pa (100 kPa), though not part of the International System of Units (SI). A pressure of 1 bar is slightly less than the current average atmospheric pressure on Earth at sea level (approximately 1.013 bar).^[1][2] 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 were introduced by the Norwegian meteorologist Vilhelm Bjerknes, who was a founder of the modern practice of weather forecasting, with the bar defined as one megadyne per square centimeter.^[3]

The SI brochure, despite previously mentioning the bar,^{[citation needed]} now omits any mention of it.^[1] The bar has been legally recognised in countries of the European Union since 2004.^[2] 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".^[4] The International Astronomical Union (IAU) also lists it under "Non-SI units and symbols whose continued use is deprecated".^[5]

Units derived from the bar include the megabar (symbol: Mbar), kilobar (symbol: kbar), decibar (symbol: dbar), centibar (symbol: cbar), and millibar (symbol: mbar).