normal weather pressure range
But the inch is really not a unit of pressure, or force per area. It is a unit of length. So a metric unit has been defined to describe normal atmospheric pressure, called a bar, and the instrument becomes a barometer.. Actually, normal average sea-level pressure is 1.01325 bars, or 1,013.25 millibars (mb).The millibar is a commonly used unit of pressure.he weight of the atmosphere on the surface of the mercury exerts a pressure transmitted through the fluid, forcing it to rise. The greater the weight, the higher the rise. The barometric pressure seldom goes above 31 inches or drops below 29 inches. Normal sea-level pressure is 29.92 inches.