Pound per square inch  

A pressure gauge reading in psi (red scale) and kPa (black scale)


Unit information  
Unit system  Imperial units, US customary units 
Unit of  Pressure, Stress 
Symbol  psi or lbf/in^{2} 
Unit conversions  
1 psi in ...  ... is equal to ... 
SI units  6.894757 kPa 
The pound per square inch or, more accurately, poundforce per square inch (symbol: lbf/in^{2};^{[1]} abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one poundforce 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.^{[2]}^{[3]} 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/in^{2}).
ksi are not widely used for gas pressures. They are mostly used in materials science, where the tensile strength of a material is measured as a large number of psi.^{[4]}
The conversion in SI Units is 1 ksi = 6.895 MPa, or 1 MPa = 0.145 ksi.
The megapound per square inch (Mpsi) is another multiple equal to a million psi. It is used in mechanics for the elastic modulus of materials, especially for metals.^{[5]}
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  

(Pa)  (bar)  (at)  (atm)  (Torr)  (psi)  
1 Pa  ≡ 1 N/m^{2}  10^{−5}  ×10^{−5} 1.0197  ×10^{−6} 9.8692  ×10^{−3} 7.5006  377×10^{−4} 1.450 
1 bar  10^{5}  ≡ 100 kPa
≡ 10^{6} dyn/cm^{2} 
1.0197  92 0.986  750.06  77 14.503 
1 at  65×10^{4} 9.806  665 0.980  ≡ 1 kp/cm^{2}  8411 0.967  735.5592  34 14.223 
1 atm  25×10^{5} 1.013  25 1.013  1.0332  1  ≡ 760  95 14.695 
1 Torr  133.3224  224×10^{−3} 1.333  551×10^{−3} 1.359  ≡ 1/760 ≈ 789×10^{−3} 1.315  ≡ 1 Torr
≈ 1 mmHg 
678×10^{−2} 1.933 
1 psi  ×10^{3} 6.8948  ×10^{−2} 6.8948  69×10^{−2} 7.030  ×10^{−2} 6.8046  93 51.714  ≡ 1 lbf /in^{2} 
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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