Definition
Pressure measured relative to the surrounding atmospheric pressure, rather than relative to a perfect vacuum. A gauge pressure reading of zero means the measured pressure is equal to the local atmospheric pressure.
Plain English
The pressure shown by a normal gauge, where zero means the same as the air pressure around you. Anything above zero is how much higher the pressure is than the outside air.
Context Anchor
Seen when reading aircraft pressure gauges, such as tire, oxygen, hydraulic, or air-system pressure indications.
Derivation
From the instrument itself: a 'gauge' is a measuring device. The term distinguishes this everyday reading from 'absolute pressure,' which is measured from a true vacuum.
Why Pilots Care
Maintenance procedures require knowing whether a reading is gauge or absolute to prevent over- or under-pressurization of critical systems.
Analogy
A tire pressure gauge does not show all the pressure inside the tire. It shows how much more pressure the tire has than the air outside it.
Grounding Statement
If a pressure gauge reads 40 psi, it means the measured pressure is 40 psi above the surrounding air pressure.
Intuition Check
Gauge pressure does not mean the total pressure present. It means pressure compared with the local outside air pressure.
Example Sentence 1
The technician inflated the main gear tire to 45 psi gauge pressure, as specified in the maintenance manual.
Example Sentence 2
Aircraft tire pressure is recorded as gauge pressure to confirm proper inflation before flight.