101325Pa

The value 101 325 Pa represents the standard atmospheric pressure at sea level, commonly referred to as one atmosphere (1 atm). The Pascal (Pa) is the SI unit of pressure, defined as one newton per square metre. It originates from the French physicist Blaise Pascal and is used globally in scientific and engineering contexts to express pressure.

Standard atmospheric pressure, 101 325 Pa, is defined by the International Union of Pure and Applied Chemistry (IUPAC) and the International Organization for Standardization (ISO) based on the mean surface pressure measured in 1913 at the gauge location of the French Association of Geodesists. Modern reference values are derived from hydrostatic equilibrium of the atmosphere and are used in the preparation of technical standards, atmospheric models, and calibration of pressure measurement devices.

In practice, 101 325 Pa is employed as a baseline in numerous fields. In aviation, the standard atmosphere model uses this pressure at sea level to derive temperature, density, and altitude relationships essential for aircraft performance calculations. In meteorology, it serves as a reference for the barometric pressure routinely measured by weather stations. Engineering disciplines, including aerospace, civil, and mechanical engineering, use it to design and test equipment that operates under normal atmospheric conditions.

While actual atmospheric pressure fluctuates with weather, geography, and altitude, 101 325 Pa remains a fixed reference value used for comparisons and calibrations. Many scientific equations, such as the ideal gas law (PV = nRT), require pressure expressed in pascals, and substituting 101 325 Pa into such formulas yields results consistent with standard sea‑level conditions. The designation 1 atm thus condenses a complex set of environmental variables into a single, internationally recognized constant.