atm

An atm (atmosphere or standard atmosphere) is a unit of pressure conceived to represent Earth atmospheric pressure. The SI effort has standardized it to be 101325 pascals which is a nominal value of the average air pressure at sea level at the latitude of Paris, France. (As such, citing a pressure in atm effectively indicates the exact number of pascals, the SI unit of pressure.) Equivalences:

• 101325 pascals.
• 1013.25 millibars.
• 1.01325 bar.
• 760 torr.
• ≈14.7 pounds-force per square inch.

Other units of pressure:

• a pascal (Pa), an SI-derived unit consisting of 1 kg·m^-1·s^-2.
• a bar, 10,000 pascals, convenient for (also) being roughly Earth atmospheric pressure.
• a millibar (mbar, 1/1000 of a bar).
• a megabar (Mbar, a million bars).
• a torr (nominal value for the pressure difference of 1 millimeter of mercury in a mercury barometer).