How to Convert From PSIA to PSIG

Written by michael judge
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How to Convert From PSIA to PSIG
Pounds per square inch is a very common unit for measurement of gas pressure. (Comstock/Comstock/Getty Images)

Engineers and mechanics typically measure pressure in units of pounds per square inch, particularly in the case of compressed gases. The abbreviation for this unit is "psi." Many pressure gauges are calibrated to read zero when exposed to atmospheric pressure, since this indicates no pressurisation. The reading from such gauges is abbreviated as "psig," for psi gauge. However, when such a gauge reads zero, the actual pressure (psia or psi absolute) is actual atmospheric pressure, or 14.7 psi. You can use this value to convert psia to psig.

Skill level:
Moderately Easy

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Things you need

  • Calculator

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  1. 1

    Enter the numerical value of your pressure reading, which is in units of psia, into the calculator. For example, if your pressure reading was 120 psia, you would enter 120.

  2. 2

    Subtract 14.7 from the value you just entered. This is the average value of atmospheric pressure at sea level and is the conversion factor between psia and psig.

  3. 3

    Report the value of the calculation as the pressure reading in units of psig. This is the value which a gauge calibrated to read zero at atmospheric pressure would display when measuring your pressure. In the case of the example, you would calculate 120 minus 14.7 to obtain 105.3 psig.

Tips and warnings

  • The metric system units for pressure are kilopascals (kPa).

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