PSI (pounds per square inch) is an imperial pressure unit equal to about 6,894.76 pascals, the standard measurement for tire pressure, compressed air systems, and hydraulic equipment in the United States. Almost every American gas station air pump and pressure washer displays ratings in PSI, making it one of the most recognized pressure units worldwide. One PSI equals approximately 0.06895 bar or 6.895 kPa.

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.