What is the definition of gage pressure?

Gage pressure is defined as the pressure measurement that is referenced from atmospheric pressure. This means it takes into account the ambient atmospheric pressure when measuring the pressure of a system. When gage pressure is measured, it reflects how much higher or lower the pressure in a system is compared to the surrounding atmosphere. For example, if a tire shows a gage pressure of 30 psi, it means that the pressure inside the tire is 30 psi greater than the atmospheric pressure.

In contrast, definitions like those involving absolute pressure or vacuum pressure don't accurately describe gage pressure. Absolute zero would suggest a reference point without any atmospheric influence, which does not apply to gage pressure. Similarly, pressure measured in a vacuum or pressures that are always negative are not applicable to the definition of gage pressure, which is specifically grounded in atmospheric conditions.