Pound per square inch
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Pounds-force per Square Inch is the pressure a material exerts on the walls of a confining vessel or enclosure. For technical accuracy, pressure must be expressed as psig (pounds-force per square inch gauge) or psia (pounds-force per square inch absolute; that is, gauge pressure plus sea level atmospheric pressure, or psig plus approximately 14.7 pounds per square inch). Also see torr which is a measurement of milimeters of Mercury, and pascals which is the SI unit.
1 psi approximately equals 6.895 kPa
See also Psi, parapsychology.