A unit of pressure is a measure of force per unit area. The most commonly used units of pressure are PSI (3 letters), Pascal (6 letters), BAR (3 letters), Kilobar (7 letters), Torr (4 letters), and Millibar (8 letters). PSI stands for pounds per square inch, Pascal is the SI unit of pressure, BAR is a metric unit of pressure, Kilobar is equal to 1000 bars, Torr is a unit of pressure equal to one millimeter of mercury, and Millibar is equal to one thousandth of a BAR.