In 1982, the International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the physical properties of substances, standard pressure should be precisely 100 kPa (1 bar). Source Wikipedia
In chemistry and in various industries, the reference pressure referred to in standard temperature and pressure (STP) was commonly 1 atm (101.325 kPa) but standards have since diverged; Source Wikipedia
