Pound per square inch

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

The pound per square inch or, more accurately, pound-force per square inch (abbreviations: psi, lbf/in², lb_f/in², lbf/sq in, lb_f/sq in) 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:

1 psi = ${\frac {1{\text{ lbf}}}{(1{\text{ in}})^{2}}}$ ≈ ${\frac {4.4482{\text{ N}}}{(0.0254{\text{ m}})^{2}}}$ ≈ 6894.757 N/m²

Therefore, one pound per square inch is approximately 6894.757 Pa.

Now converting the psi to standard atmospheres:

1 atm = $101325{\text{ Pa}}$ = ${\frac {101325}{6894.757293168}}$ ≈ 14.70 psi

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 gage (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.^[1]^[2] When gauge pressure is referenced to something other than ambient atmospheric pressure, then the units would be pounds per square inch differential (psid).

Multiples

The kilopound per square inch (ksi) is a scaled unit derived from psi, equivalent to a thousand psi.

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.^{[citation needed]}

The conversion in SI Units is 1 ksi = 6.895 MPa

The megapound per square inch (Mpsi) is an other multiple equivalent to a million of psi. It is used in Mechanics for the elastic modulus of the materials, especially for metals.^[3]

The conversion in SI Units is 1 Mpsi = 6.895 GPa

Magnitude

Inch of water: 0.036 psi
Blood pressure – clinically normal human blood pressure (120/80 mmHg): 2.32 psi/1.55 psi
Natural gas residential piped in for consumer appliance; 4-6 psi.
Boost pressure provided by an automotive turbocharger (common): P_g = 6–15 psi
NFL football: P_g = 12.5–13.5 psi
Atmospheric pressure at sea level (standard): P_a = 14.7 psi
Automobile tire overpressure (common): P_g = 32 psi
Bicycle tire overpressure (common): P_g = 65 psi
Workshop or garage air tools: P_g = 90 psi
Air brake (rail) or air brake (road vehicle) reservoir overpressure (common): 90 psi ≤ P_g ≤ 120 psi
Road racing bicycle tire overpressure: P_g = 120 psi
Steam locomotive fire tube boiler (UK, 20th century): 150 psi ≤ P_g ≤ 280 psi
Union Pacific Big Boy steam locomotive boiler: 300 psi
Natural gas pipelines: 800 to 1000 psi
Full SCBA (self-contained breathing apparatus) for IDLH (non-fire) atmospheres: 2216 psi
Full SCUBA (self-contained underwater breathing apparatus) tank overpressure (common): P_g = 3000 psi
Full SCBA (self-contained breathing apparatus) for interior firefighting operations: 4500 psi
Airbus A380 hydraulic system: 5000 psi
Ultimate strength of ASTM A36 steel: 58,000 psi
Water jet cutter: 40,000–100,000 psi

Conversions

Pressure units
v t e	Pascal	Bar	Technical atmosphere	Standard atmosphere	Torr	Pound per square inch
v t e	(Pa)	(bar)	(at)	(atm)	(Torr)	(lbf/in²)
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 at	98066.5	0.980665	—	0.9678411053541	735.5592401	14.2233433071203
1 atm	≡ 101325	≡ 1.01325	1.0332	—	760	14.6959487755142
1 Torr	133.322368421	0.001333224	0.00135951	⁠1/760⁠ ≈ 0.001315789	—	0.019336775
1 lbf/in²	6894.757293168	0.068947573	0.070306958	0.068045964	51.714932572	—

References

^ "Glossary of Industrial Air Cleaning Technology". United Air Specialists, Inc. Archived from the original on August 1, 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ "Gage v. Sealed v. Absolute pressure" (PDF). Dynisco.
^ An example of the use of Mpsi in Mechanics for the elastic moduli of several materials

External links

[1] "Glossary of Industrial Air Cleaning Technology". United Air Specialists, Inc. Archived from the original on August 1, 2011. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[2] "Gage v. Sealed v. Absolute pressure" (PDF). Dynisco.

[3] An example of the use of Mpsi in Mechanics for the elastic moduli of several materials

[1]

[2]

[3]

Multiples

Magnitude

Conversions

See also

References

External links