What is the Difference Between Absolute Pressure and Gauge Pressure?

The difference between absolute pressure and gauge pressure lies in their reference points and the way they are measured:

• Absolute Pressure: This is the pressure measured relative to a perfect vacuum or zero pressure in the empty, air-free space of the universe. It is denoted with the subscript "abs" (Pabs) and is always definite, independent of environmental influences such as weather or altitude.
• Gauge Pressure: This is the pressure measured relative to atmospheric pressure. It is denoted with the subscript "e" (Pe) and is calculated as follows: Pe = Pabs - Pamb (atmospheric pressure). Gauge pressure is positive for pressures above atmospheric pressure and negative for pressures below it. It is commonly used for practical applications, as it simplifies measurements by using atmospheric pressure as its zero point.

In summary, absolute pressure measures the pressure relative to a perfect vacuum, while gauge pressure measures the pressure relative to atmospheric pressure. Due to varying atmospheric pressure, gauge pressure measurements may not be as precise as absolute pressure measurements, which are always definite.

Comparative Table: Absolute Pressure vs Gauge Pressure

The difference between absolute pressure and gauge pressure can be summarized in the following table:

To convert between absolute pressure and gauge pressure, you can use the formulas mentioned in the table. For example, to find the absolute pressure from the gauge pressure, add the local atmospheric pressure value. Conversely, to find the gauge pressure from the absolute pressure, subtract the local atmospheric pressure value.