What must be added to gauge pressure to obtain absolute pressure?

To convert gauge pressure to absolute pressure, atmospheric pressure must be added. Gauge pressure is measured relative to the ambient atmospheric pressure; it indicates how much pressure is present in a system above the surrounding atmospheric pressure.

Absolute pressure, on the other hand, is the total pressure at a given point and is measured relative to a perfect vacuum. By adding atmospheric pressure to gauge pressure, you account for the pressure exerted by the atmosphere, thereby accurately determining the absolute pressure in the system.

This relationship is key in various applications, including thermodynamics and fluid mechanics, where an understanding of absolute pressure is critical for ensuring accurate calculations and safe operation of equipment.