<P> Atmospheric pressure, sometimes also called barometric pressure, is the pressure within the atmosphere of Earth (or that of another planet). In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point . As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation . Pressure measures force per unit area, with SI units of Pascals (1 pascal = 1 newton per square metre, 1 N / m). On average, a column of air with a cross-sectional area of 1 square centimetre (cm), measured from mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons or 2.37 lb, resulting in a pressure at sea level of about 10.1 N / cm or 101 kN / m (101 kilopascals, kPa). A column of air with a cross-sectional area of 1 in (6.45 cm) would have a mass of about 6.65 kg and a weight of about 65.4 N or 14.7 lb, resulting in a pressure of 10.1 N / cm or 14.7 lb / in . In the United States, atmospheric pressure near sea level is commonly rounded to 15 lb / in, and expressed as "15 psi" (15 pounds per square inch .) </P> <Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (September 2017) (Learn how and when to remove this template message) </Td> </Tr> </Table>

Atmospheric pressure at sea level in si units