Pounds Per Square Inch

Perhaps it should be PPSI? Perhaps it stands for something else entirely! Actually...The pound per square inch or, more accurately, pound-force per square inch (symbol: psi or lbf/in2 or lbf/in2 or lbf/sq in or lbf/sq in) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch:

One pound per square inch approximately equals 6,894.757 Pa.

So there!