What is absolute pressure defined as?

Absolute pressure is defined as the pressure measured relative to a vacuum, meaning it incorporates atmospheric pressure in addition to any gauge pressure present. Gauge pressure measures the pressure relative to the surrounding atmospheric pressure, which can lead to confusion if not properly contextualized. To find absolute pressure, you add the gauge pressure (the pressure in the system) to atmospheric pressure (the atmospheric force exerted on the surface of the liquid or gas in the system).

This is critical in many applications, such as in fluid mechanics and thermodynamics, to ensure that calculations reflect true pressure conditions without being influenced by changes in atmospheric pressure. Thus, when evaluating absolute pressure, it is essential to include both atmospheric pressure and gauge pressure to arrive at the correct value.