What is the unit of measure for negative gauge pressure?

Negative gauge pressure refers to a pressure measurement that is below atmospheric pressure. In many industrial applications, especially in the context of instrumentation and process control, it is often expressed in terms of a column of liquid.

Inches of water column is commonly used as a unit of measure for low pressures, including negative gauge pressures. This is because it provides a practical way to visualize the pressure in terms of how high a column of water would rise or fall compared to atmospheric pressure. A negative gauge pressure indicates that the measured pressure is less than atmospheric pressure, and representing this in inches of water column allows for easy interpretation and comparison in many applications.

The other units of measure listed—Pascal, PSI, and Bar—are typically used for absolute pressure or positive gauge pressure measurements. While these can technically represent negative gauge pressures if expressed in a specific context, inches of water column is more directly associated with indicating pressure variations, including negative values, in a relatable format for practitioners in fields like HVAC, plumbing, and process environments.