Atmospheric pressure is the
pressure at any point in the
Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the
hydrostatic pressure caused by the
weight of
air above the measurement point. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location. Similarly, as elevation increases there is less overlying atmospheric mass, so that pressure decreases with increasing elevation. A column of air 1 square inch in cross section, measured from
sea level to the top of the atmosphere, would weigh approximately 14.7
lbf. A 1 m² (11 sq ft) column of air would weigh about 100
kilonewtons (equivalent to a mass of 10.2
tonnes at the surface).
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