Pounds per square inch
|Pound per square inch|
|Symbol||psi or lbf/in2|
|1 psi in ...||... is equal to ...|
The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2;
 abbreviation: psi) is a unit of
Pounds per square inch absolute (psia) is used to make it clear that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi, this will be added to any pressure reading made in air at sea level. The converse is pounds per square inch gauge (psig), indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psig in a local atmospheric pressure at sea level (14.7 psia) will have a pressure of 79.7 psia (14.7 psi + 65 psi).   When gauge pressure is referenced to something other than ambient atmospheric pressure, then the units would be pounds per square inch differential (psid).
The kilopound per square inch (ksi) is a scaled unit derived from psi, equivalent to a thousand psi (1000 lbf/in2).
The conversion in SI Units is 1 ksi = 6.895 MPa, or 1 MPa = 0.145 ksi.
The conversion in SI Units is 1 Mpsi = 6.895 GPa, or 1 GPa = 0.145 Mpsi.