Standard atmosphere

$atm$ = 101 325 Pa

Value: 101 325 Pa
Standard uncertainty: exact
Relative uncertainty: exact
Status: Exact: conventional value adopted in 1954
Symbol: $atm$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# standard atmosphere, CODATA 2022 (NIST)
standard_atmosphere = 1.01325e5  # Pa, exact

# SciPy: scipy.constants.physical_constants['standard atmosphere']

What it is

A pressure of exactly 101 325 pascals, adopted in 1954 as a reference close to average sea-level air pressure. It defines the non-SI unit atm, and through it the torr (1/760 atm).

Equations

$1 atm = 101 325 Pa$ definition

In other units

Unit	Value
CGS (cm⁻¹ g s⁻²)	1 013 250	exact
hPa hectopascal	1013.25	exact
kPa kilopascal	101.325	exact
MPa megapascal	0.101 325	exact
bar bar	1.013 25	exact
mbar millibar	1013.25	exact
atm standard atmosphere	1	exact
Torr torr	760	exact
mmHg millimetre of mercury	759.999 8917	exact
psi pound per square inch	14.695 948 78	exact
dyn/cm² dyne per square centimetre	1 013 250	exact

Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display.

How the value changed, 1998–2022

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	101 325	exact	exact
2018	101 325	exact	exact
2014	101 325	exact	exact
2010	101 325	exact	exact
2006	101 325	exact	exact
2002	101 325	exact	exact
1998	101 325	exact

“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).

Related constants

Adopted exact

p^∘

Standard-state pressure 100 000 Pa Physico-chemical exact

V_{m}

Molar volume of ideal gas 22.413 969 54… × 10⁻³ m³ mol⁻¹