Standard Atmosphere (atm)

Metric (SI)Current unit

Exactly 101,325 pascals, the average pressure of the atmosphere at sea level.

1 standard atmosphere = 101,325 pascals (exactly).

About the standard atmosphere

A column of mercury about 76 cm tall was Torricelli's measure of the air, and the standard atmosphere began as exactly that: the pressure of 760 mm of mercury at 0 degrees Celsius under standard gravity. It was used as a reference for physical and chemical properties, and the Celsius scale set 100 degrees as the boiling point of water at that pressure.

In 1954 the 10th CGPM confirmed the standard atmosphere as exactly 1,013,250 dynes per square centimeter, which is 101,325 pascals, a definition that no longer depends on the properties of any substance.

In practice one atmosphere is about 1.01325 bar, 760 mmHg, 14.696 psi or 29.92 inHg, and roughly the pressure of 10.33 meters of water. Chemistry splits on it: until 1982 standard temperature and pressure used 1 atm, but that year IUPAC recommended a standard pressure of exactly 100 kPa instead.

Sources: Wikipedia: Standard atmosphere (unit); Wikipedia: Atmospheric pressure; Wikipedia: Evangelista Torricelli

Standard Atmosphere conversion chart

1 standard atmosphere expressed in every other pressure unit:

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• pascal (pressure)
• kilopascal (pressure)
• hectopascal (pressure)
• megapascal (pressure)
• gigapascal (pressure)
• bar (pressure)
• millibar (pressure)
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• kilometer (length)
• centimeter (length)
• millimeter (length)
• micrometer (length)
• nanometer (length)
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• decimeter (length)
• hectometer (length)

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