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 millimeter of mercury (mmHg) is a pressure unit equal to about 133.322 pascals, traditionally used in medicine for measuring blood pressure and in meteorology for barometric readings. A normal adult blood pressure of 120/80 mmHg is universally understood by healthcare professionals, making this unit a fixture in clinical settings. One mmHg equals approximately 0.01934 psi or 0.1333 kPa.