What is high or low barometric pressure? Adjusted to sea level, a pressure reading above 30.2 inHg is considered to be high pressure, and below 29.8 inHg is considered low. Most of the time, in human-inhabited places, the barometric pressure will stay close to the normal range (29.8 inHg-30.2 inHg), and will rarely exceed 30.5 inHg or fall below 29.4 inHg. The average barometric pressure is 29.92 inHg (or 1 atmosphere!). In summary:

High Pressure: above 30.2 inHg
Normal Range: 29.8 inHg - 30.2 inHg
Low Pressure: below 29.8 inHg