Negative Gauge Pressure

The gauge pressure is stated as either a vacuum or negative gauge pressure when it is lower than the atmospheric pressure. Negative Gauge Pressure is the difference in pressure between any vacuum and atmospheric pressure.

The maximum possible negative gauge pressure is always limited by the current ambient atmospheric pressure, which constantly varies, but is typically around 1 bar absolute.

It is certainly possible to have a negative gauge pressure, but not possible to have a negative absolute pressure. For instance, an absolute pressure of 80 kPa may be described as a gauge pressure of −21 kPa (i.e., 21 kPa below an atmospheric pressure of 101 kPa).