Pounds 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 (symbol: psi or lbf/in² or lb_f/in² or lbf/sq in or lb_f/sq in)/ pressure per square inch 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:

Using unit conversion:

1 psi = $\frac{1 \text{ lbf}} {(1 \text{ in})^2} = \frac{4.4482216152605 \text{ N}} {(0.0254 \text{ m})^2}$ ≈ 6894.757293168 N/m²

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

Now converting the psi to standard atmospheres:

$\frac{1 \text{ psi}}{ 6894.757293 \text{ Pa}} \cdot \frac{1.01325 \text { x} \ 10^5 \text{ Pa}}{1 \text{ atm}}$ ≈ 14.69594877551 psi/atm

Therefore, 1 atmosphere is approximately 14.696 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 atmospheric pressure, will have a pressure of 65 + 14.7 = 79.7 psia or 65 psig.^[1]^[2]

1 ksi
2 Magnitude
3 Conversions
4 See also
5 References
6 External links

[edit] ksi

The kilopound per square inch 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 an inconveniently large number of psi.

[edit] Magnitude

Main article: Orders of magnitude (pressure)

In liquid: pressure per square inch (psi)

Blood Pressure – Average human blood pressure (120/80): 2.32psi/1.55psi
Water jet cutter: 40,000–100,000 psi
Commercial jet airliner hydraulic pressure: 3000 psi
Boost Pressure Provided By an Automotive Turbocharger(common):P_g = 6–15psi
Atmospheric pressure at sea level (standard): P_a = 14.7 psi
Automobile tyre overpressure (common): P_g = 32 psi
Bicycle tyre 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 toxic atmospheres: 2216 psi
Full scuba tank overpressure (common): P_g = 3000 psi
Airbus A380 hydraulic system: 5000 psi
Ultimate strength of ASTM A36 steel: 58,000 psi
Inch of water: 0.036 psi

[edit] Conversions

Pressure units
v t e	Pascal	Bar	Technical atmosphere	Standard atmosphere	Torr	Pounds per square inch
v t e	(Pa)	(bar)	(at)	(atm)	(Torr)	(psi)
1 Pa	≡ 1 N/m²	10⁻⁵	1.0197×10⁻⁵	9.8692×10⁻⁶	7.5006×10⁻³	1.450377×10⁻⁴
1 bar	10⁵	≡ 10⁶ dyn/cm²	1.0197	0.98692	750.06	14.50377
1 at	0.980665 ×10⁵	0.980665	≡ 1 kp/cm²	0.9678411	735.5592	14.22334
1 atm	1.01325 ×10⁵	1.01325	1.0332	≡ p₀	≡ 760	14.69595
1 Torr	133.3224	1.333224×10⁻³	1.359551×10⁻³	1.315789×10⁻³	≈ 1 mm_Hg	1.933678×10⁻²
1 psi	6.8948×10³	6.8948×10⁻²	7.03069×10⁻²	6.8046×10⁻²	51.71493	≡ 1 lb_F/in²