Bar (unit)

The bar (symbol: bar or b) is a unit of pressure. They are not SI units, but they are still used in descriptions of pressure. Although the use of those units is discouraged, the bar is about the same as atmospheric pressure.

Multiples

Main article: SI prefix

The bar, the decibar, and the millibar are known as:

• 1 bar = 100 000 pascals (Pa) = 1,000,000 dynes per square centimeter (baryes)
• 1 dbar = 0.1 bar = 10 000 Pa = 100,000 dyn/cm²
• 1 cbar = 0.01 bar = 1000 Pa
• 1 mbar = 0.001 bar = 100 Pa = 1,000 dyn/cm²

(The pascal is one newton per square meter.)

Origin

The word bar has its origin in the Greek word βάρος (baros), meaning weight. Its official symbol is "bar"; the earlier "b" is no longer used but is still often seen especially as "mb," rather than "mbar" for millibars.

The bar and the millibar were defined by Sir Napier Shaw in 1909 and became used internationally in 1929.

Other websites

• Official SI website: Table 8. Non-SI units accepted for use with the SI Archived 2008-08-21 at the Wayback Machine
• Conversion factors from bar to various pressure units