Pound Per Square Inch (psi)

US & ImperialCurrent unit

About 6,894.757 pascals. The common unit for tire pressure, hydraulics and gas pipelines in the US.

1 pound per square inch = 6,894.757293 pascals (approximately).

About the pound per square inch

Unlike most pressure units, psi has no namesake: it simply spells out its own definition, one pound-force acting on one square inch, and it is based on avoirdupois units. Used mainly in the United States, it is about 6.895 kilopascals.

The letters after the unit matter. Psia is measured against a vacuum, while psig is measured against the surrounding air, so at sea level, where the atmosphere is about 14.7 psi, you add that amount to a gauge reading to get an absolute one. A bicycle tire at 65 psig is therefore at 79.7 psia, and the label psid means a difference between two pressures rather than a reference to ambient air.

Typical automobile tires are listed at about 32 psig, and road racing bicycle tires at about 120 psig. One standard atmosphere is 14.696 psi, which gives a feel for how many multiples of sea-level air those tire pressures represent.

Sources: Wikipedia: Pounds per square inch; Wikipedia: Standard atmosphere (unit)

Pound Per Square Inch conversion chart

1 pound per square inch expressed in every other pressure unit:

More US & Imperial units

• kilopound per square inch (pressure)
• inch of mercury (pressure)
• inch of water (pressure)
• pound per square foot (pressure)
• inch (length)
• foot (length)
• yard (length)
• mile (length)
• thou (length)
• league (length)
• furlong (length)
• chain (length)
• rod (length)
• link (length)
• hand (length)
• pound (weight & mass)

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