What is considered low barometric pressure?

Barometric pressure of under 29.50 inches of mercury at sea level is considered low. At sea level, a normal barometer reading is between about 29.70 inches of mercury and 30.20 inches.

Barometric pressure drops with altitude, so pressure at one altitude may appear higher at a lower altitude. In reading a barometer, however, the trend in readings is more important than the reading itself. If barometer readings are consistently falling that may mean a storm is coming. Sunny conditions may be indicated by barometer readings that are steadily rising. An exception to this occurs during exceptionally low readings, which may indicate the approach of a severe storm, regardless of the overall trend.