Atmosphere (atm)

The standard atmosphere (atm) is defined as exactly 101 325 Pa, approximately the mean air pressure at sea level.

Symbol: atm

Quantity: pressure, stress and differential pressure (force per unit area)

SI relation: 1 atm = 101325 Pa (exact)

Derivation: 1 atm = 101 325 Pa (exact, by definition)

Exact: yes, by definition

History

The 10th CGPM fixed the standard atmosphere at 101 325 Pa in 1954. It is not an SI unit, but it is still used for reference conditions and gas laws.

Typical uses

Chemistry and gas laws (STP and NTP conditions)
Diving: each 10 m of seawater adds ≈ 1 atm
Autoclaves and pressure vessels described in atmospheres

Convert atmospheres to other units

1 atm in other pressure units
Conversion	1 atm equals	Reverse
atmosphere to pascal	101325 Pa	pascal to atmosphere
atmosphere to kilopascal	101.325 kPa	kilopascal to atmosphere
atmosphere to psi	14.69594878 psi	psi to atmosphere
atmosphere to bar	1.01325 bar	bar to atmosphere
atmosphere to millimeter of mercury	759.9998917 mmHg	millimeter of mercury to atmosphere
atmosphere to inch of water	406.7824617 inH₂O	inch of water to atmosphere
atmosphere to megapascal	0.101325 MPa	megapascal to atmosphere
atmosphere to millibar	1013.25 mbar	millibar to atmosphere
atmosphere to torr	760 Torr	torr to atmosphere
atmosphere to millimeter of water	10332.27453 mmH₂O	millimeter of water to atmosphere
atmosphere to centimeter of water	1033.227453 cmH₂O	centimeter of water to atmosphere
atmosphere to inch of mercury	29.92125558 inHg	inch of mercury to atmosphere
atmosphere to decibar	10.1325 dbar	decibar to atmosphere
atmosphere to inch of water (60 °F)	407.1893586 inH₂O (60 °F)	inch of water (60 °F) to atmosphere
atmosphere to barye	1013250 Ba	barye to atmosphere

Open the Pressure Converter to convert any value between all units.

Sources

Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "atmosphere, standard (atm)".

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.

Cite this page

APA

Scientific Converters. (2026, October 15). Atmosphere (atm). Retrieved October 17, 2026, from https://scientificconverters.com/units/atmosphere/

IEEE

Scientific Converters, "Atmosphere (atm)," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/units/atmosphere/