The standard atmosphere (atm) is a pressure unit defined as exactly 101,325 pascals, representing the average atmospheric pressure at sea level on Earth. It serves as a reference point in chemistry for gas law calculations and in engineering for rating pressure vessel capacities. One atmosphere equals approximately 1.01325 bar, 14.696 psi, or 760 mmHg.

The torr is a pressure unit named after Evangelista Torricelli, equal to approximately 133.322 pascals, used primarily in vacuum physics and high-altitude research. It is nearly identical to the millimeter of mercury, with one torr defined as exactly 1/760 of a standard atmosphere. Vacuum pumps, electron microscopes, and semiconductor manufacturing equipment commonly specify operating pressures in torr.