The standard atmosphere (symbol: atm) is a unit of pressure defined as 1,013.25 mbar (101,325 Pa; 1,013.25 hPa), equivalent to 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. ... A column of air with a cross-sectional area of 1 in2 would have a weight of about 14.7 lbf, resulting in a pressure of 14.7 lbf/in2.
