Pound per square inch

<p>The pound per square inch (abbreviation: psi) or, more accurately, pound-force per square inch (symbol: lbf/in2), is a <a href="/facts/Unit_of_measurement/pvTpWbmC">unit of measurement</a> of <a href="/facts/Pressure/eyc37GRG">pressure</a> or of <a href="/facts/Stress_(mechanics)/ErAXDbbd">stress</a> based on <a href="/facts/Avoirdupois/0R7uruYE">avoirdupois</a> units and used primarily in the United States. It is the pressure resulting from a <a href="/facts/Force_(physics)/LNAUWMwK">force</a> with magnitude of one <a href="/facts/Pound-force/w62gn6Y0">pound-force</a> applied to an area of one <a href="/facts/Square_inch/HMKj3Jok">square inch</a>. In <a href="/facts/SI_units/S7YLglNz">SI units</a>, 1 psi is approximately 6,895 <a href="/facts/Pascal_(unit)/Am1To2Qm">pascals</a>.
</p><p>The pound per square inch absolute (psia) is used to make it clear that the pressure is relative to a <a href="/facts/Vacuum/BTk3goyV">vacuum</a> rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi (101 <a href="/facts/Pascal_(unit)/Am1To2Qm">kilopascals</a>), this will be added to any pressure reading made in air at <a href="/facts/Sea_level/mDhuI7Xe">sea level</a>. The converse is pound per square inch gauge (psig), indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psig in a local atmospheric pressure at sea level (14.7 psi) will have a pressure of 79.7 psia (14.7 psi + 65 psi). When gauge pressure is referenced to something other than ambient atmospheric pressure, then the unit is pound per square inch differential (psid).
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Pound per square inch open-in-new

Pound per square inch