|Pound per square inch|
|Unit system||Imperial units, US customary units|
|Unit of||Pressure, Stress|
|Symbol||psi or lbf/in2|
|1 psi in ...||... is equal to ...|
|SI units||6.894757 kPa|
The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) 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:
Therefore, one pound per square inch is approximately 6894.757 Pa.
Now converting the psi to standard atmospheres:
Therefore, 1 atmosphere is approximately 14.7 pounds per square inch.
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 or pounds per square inch gauge (psig), indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psi above local atmospheric pressure (say, 14.7 psia locally), will have a pressure of 65 + 14.7 = 79.7 psia or 65 psig. 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.
|Pascal||Bar||Technical atmosphere||Standard atmosphere||Torr||Pounds per square inch|
|1 Pa||≡ 1 N/m2||10−5||×10−51.0197||×10−69.8692||×10−37.5006||377×10−41.450|
|1 bar||105||≡ 100 kPa
≡ 106 dyn/cm2
|1 at||65×1049.806||6650.980||≡ 1 kp/cm2||84110.967||735.5592||3414.223|
|1 atm||25×1051.013||251.013||1.0332||1||≡ 760||9514.695|
|1 Torr||133.3224||224×10−31.333||551×10−31.359||≡ 1/760 ≈ 789×10−31.315||≡ 1 Torr
≈ 1 mmHg
|1 psi||×1036.8948||×10−26.8948||69×10−27.030||×10−26.8046||9351.714||≡ 1 lbf /in2|
A metal’s yield strength and ultimate tensile strength values are expressed in tons per square inch, pounds per square inch or thousand pounds (KSI) per square inch. For example, a tensile strength of a steel that can withstand 40,000 pounds of force per square inch may be expressed as 40,000 PSI or 40 KSI (with K being the [multiplier] for thousands of pounds). The tensile strength of steel may also be shown in MPa, or megapascal.
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