Pounds per square inch

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:

Contents

• Multiples
• Magnitude
• References

1   psi = 1   lbf ( 1   in ) 2 ≈ 4.4482   N ( 0.0254   m ) 2 ≈ 6894.757   N / m 2

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

Now converting the psi to standard atmospheres:

1   atm = 101325   Pa = 101325   Pa 6894.757293168   Pa / psi ≈ 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. When gauge pressure is referenced to something other than ambient atmospheric pressure, then the units would be pounds per square inch differential (psid).