|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. In SI units, 1 psi is approximately equal to 6895 Pa.
The pound 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 (101 kilopascals), this will be added to any pressure reading made in air at sea level. The converse is pound 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 psi) 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 unit would be pound 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.
- Inch of water: 0.036 psid
- Blood pressure – clinically normal human blood pressure (120/80 mmHg): 2.32 psig/1.55 psig
- Natural gas residential piped in for consumer appliance; 4–6 psig.
- Boost pressure provided by an automotive turbocharger (common): 6–15 psig
- NFL football: 12.5–13.5 psig
- Atmospheric pressure at sea level (standard): 14.7 psia
- Automobile tire overpressure (common): 32 psig
- Bicycle tire overpressure (common): 65 psig
- Workshop or garage air tools: 90 psig
- Air brake (rail) or air brake (road vehicle) reservoir overpressure (common): 90–120 psig
- Road racing bicycle tire overpressure: 120 psig
- Steam locomotive fire tube boiler (UK, 20th century): 150–280 psig
- Union Pacific Big Boy steam locomotive boiler: 300 psig
- US Navy steam boiler pressure: 800 psi
- Natural gas pipelines: 800–1000 psig
- Full SCBA (self-contained breathing apparatus) for IDLH (non-fire) atmospheres: 2216 psig
- Nuclear reactor primary loop: 2300 psi
- Full SCUBA (self-contained underwater breathing apparatus) tank overpressure (common): 3000 psig
- Full SCBA (self-contained breathing apparatus) for interior firefighting operations: 4500 psig
- Airbus A380 hydraulic system: 5000 psig
- Land Rover Td5 diesel engine fuel injection pressure: 22,500 psi
- Ultimate strength of ASTM A36 steel: 58,000 psi
- Water jet cutter: 40,000–100,000 psig
As the pascal is a very small unit relative to industrial pressures, the kilopascal is commonly used. 1000 kPa ≈ 145 lbf/in2.
Approximate conversions (rounded to some arbitrary number of digits, except when denoted by "≡") are shown in the following table.
|Pascal||Bar||Technical atmosphere||Standard atmosphere||Torr||Pound per square inch|
|1 Pa||—||1 Pa = 10−5 bar||1 Pa = 1.0197×10−5 at||1 Pa = 9.8692×10−6 atm||1 Pa = 7.5006×10−3 Torr||1 Pa = 0.000145037737730 lbf/in2|
|1 bar||105||—||= 1.0197||= 0.98692||= 750.06||= 14.503773773022|
|1 atm||≡ 101325||≡ 1.01325||1.0332||—||760||14.6959487755142|
|1 Torr||133.322368421||0.001333224||0.00135951||1/760 ≈ 0.001315789||—||0.019336775|
- IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units), IEEE Std 260.1™-2004 (Revision of IEEE Std 260.1-1993)
- "Glossary of Industrial Air Cleaning Technology". United Air Specialists, Inc. Archived from the original on August 1, 2011.
- "Gage v. Sealed v. Absolute pressure" (PDF). Dynisco.
- "Tensile Strength of Steel and Other Metals". All Metals & Forge Group. 18 April 2013. Retrieved 2016-07-26.
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.
- "An example of the use of Mpsi in mechanics for the elastic moduli of several materials". Archived from the original on 2016-12-16. Retrieved 2015-06-06.
- BS 350: Part 1: 1974 – Conversion factors and tables. British Standards Institution. 1974. p. 49. ISBN 0-580-08471-X.
- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI) (PDF). National Institute of Standards and Technology. 2008. p. 66.