Relative pressure or gauge pressure is pressure as compared to atmospheric pressure, or the average pressure of air at Earth's sea level — 101.325 kPa, or 1 atm. Therefore, the relative pressure of ambient air at sea level is usually close to zero.

A total vacuum, with absolute pressure of zero, would have relative pressure of -1 atm. Likewise, a gas at absolute pressure of 10 atm would have a relative pressure of 9 atm.

Introductory physics

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