what does atm stand for in chemistry

In chemistry, **atm** is the abbreviation for the **standard atmosphere**, which is a unit of pressure. This unit represents the average atmospheric pressure at sea level. One standard atmosphere is precisely defined as 101,325 Pascals (Pa) or 760 millimeters of mercury (mmHg). It is often used as a standard reference condition, such as in the definition of Standard Temperature and Pressure (STP), for calculations involving gases and to understand their behavior under various conditions.