Pounds per square in gauge, or psig, is a measure of pressure, specifically it is a gauge pressure. This means that it is measured with respect to the atmospheric pressure.[1] Psig is used in contrast to psia, which is pounds per square inch absolute, measured with respect to vacuum. This can all be visualized in Figure 1.

For example, a bike tire may be 65 psi above atmospheric pressure which is its psig value, and if the atmospheric pressure is 14.7 psi, then its psia value would be 65 + 14.7 = 79.7 psia.

Figure 1: Possible pressure measurements of a system.[2]


  1. Measurement Unit Converter. (May 7, 2015). Psig [Online]. Available:
  2. Created internally by a member of the Energy Education team.

Authors and Editors

Jordan Hanania, Kailyn Stenhouse, Jason Donev
Last updated: August 26, 2015
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