Bar

Metric (SI)Current unit

Exactly 100,000 pascals, close to atmospheric pressure at sea level. Used for tire pressure, diving and industrial gauges.

1 bar = 100,000 pascals (exactly).

About the bar

Bar began as a name that meant different things to different people. It comes from the Ancient Greek baros, weight, and from 1793 to 1795 an early metric system used bar for a unit of mass equal to the modern tonne. The pressure bar was introduced by the Norwegian meteorologist Vilhelm Bjerknes, a founder of modern weather forecasting, who defined it as one megadyne per square centimeter. Some earlier writers had used bar for one dyne per square centimeter, a source of confusion.

The bar is a metric unit but not part of the SI, and its official symbol is simply bar, since the old b clashes with the barn and the bit. It has been legally recognized in EU countries since 2004, although NIST deprecates it except for limited use in meteorology.

Its size is handy because 1 bar is slightly less than average sea-level pressure, which is about 1.013 bar. In scuba diving every 10 meters of seawater adds about 1 bar and a full standard tank holds about 200 bar. Tire pressure and turbocharger boost are often quoted in bar outside the US.

Sources: Wikipedia: Bar (unit); Wikipedia: Atmospheric pressure

Bar conversion chart

1 bar expressed in every other pressure unit:

More Metric (SI) units

• pascal (pressure)
• kilopascal (pressure)
• hectopascal (pressure)
• megapascal (pressure)
• gigapascal (pressure)
• millibar (pressure)
• standard atmosphere (pressure)
• meter (length)
• kilometer (length)
• centimeter (length)
• millimeter (length)
• micrometer (length)
• nanometer (length)
• picometer (length)
• decimeter (length)
• hectometer (length)

All Metric (SI) units

Browse all pressure units.