A vacuum is commonly measured in which unit?

The unit of measurement for vacuum that is most commonly referenced is inches of mercury (inHg). This unit comes from the practice of measuring the height of a column of mercury that a particular pressure can support. In the context of vacuum measurement, it indicates how much lower the pressure is compared to the atmospheric pressure. A perfect vacuum would be represented by 0 inches of mercury, while higher values indicate less vacuum (i.e., closer to atmospheric pressure).

Although Pascals, atmospheres, and millibars can also be used to measure pressure, inches of mercury is a traditional and widely accepted method, particularly in many industries related to refrigeration and HVAC. It provides a clear and practical visualization related to how vacuum conditions change in relation to the atmospheric pressure, which is critical for understanding processes in refrigeration systems.