Pound-force per square inch

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The abbreviation psi has multiple meanings; see Psi for other possibilities.

The pound-force per square inch (symbol: lbf/in²) is a non-SI unit of pressure based on avoirdupois units. In casual English language use it is rendered as "pounds per square inch", abbreviated to psi with little distinction between "mass" and "force"

1 Definition
2 Context
3 See also
4 External links

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Definition

At 1 lbf/in², a force of one pound-force is applied to an area of one square inch.

1 lbf/in² = 6 894.75729 pascals (Pa)

Other abbreviations are used that append a modifier to "psi". However, the National Institute of Standards and Technology recommends that, to avoid confusion, any modifiers be instead applied to the quantity being measured rather than the unit of measure[1] For example, "P_g = 100 psi" rather than "P = 100 psig".

psia (pounds-force per square inch absolute) - gauge pressure plus local atmospheric pressure. Replace "x psia" with "P_a = x psi".
psid (psi difference) - difference between two pressures. Replace "x psid" with "ΔP = x psi".
psig (pounds-force per square inch gauge). Replace "x psig" with "P_g = x psi".
psivg (psi vented gauge) - difference between the measuring point and the local pressure. Replace "x psivg" with "P_vg = x psi".
psisg (psi sealed gauge) - difference between a chamber of air sealed at atmospheric pressure and the pressure at the measuring point. Replace "x psisg" with "P_sg = x psi".

The ksi (kip, "kilo-pound per square inch") is defined as 1000 psi, combining the prefix kilo with the psi abbreviation. It is occasionally seen in materials science and mechanical engineering, where it is used to specify stress and Young's modulus.

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