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Standard atmosphere

patm=101,325 Pap_{\mathrm{atm}} = 101,325\ \text{Pa}
Value101.325 kPa (101,325 Pa)
Use in the calculator →
StatusExact by definition: no uncertainty
Source10th CGPM (1954); SI Brochure, 9th edition
CategoriesThermodynamicEngineering & Trade
Standard atmosphere in every pressure unit
UnitValue
kilopascal101.325 kPa
pound per square foot2,116.2166 lb/ft²
pound per square inch14.695949 psi
bar1.01325 bar
atmosphere1 atm
millimeter of water column10,332.275 mmH₂O
centimeter of water column1,033.2275 cmH₂O
hectopascal1,013.25 hPa
17 more pressure units
microbar1,013,250 μbar
barye1,013,250 Ba
millitorr760,000 mTorr
pascal101,325 Pa
millibar1,013.25 mbar
torr760 Torr
millimeter of mercury759.99989 mmHg
inch of water column406.78246 in w.g.
foot of water column33.898539 ft H₂O
inch of mercury29.921256 inHg
meter of water column10.332275 m H₂O
decibar10.1325 dbar
kilogram-force per square centimeter1.0332275 kgf/cm²
megapascal0.101325 MPa
kip per square inch0.014695949 ksi
gigapascal0.000101325 GPa
million pounds per square inch0.000014695949 Mpsi

Learning zone

The standard atmosphere is a defined unit, not a measurement: exactly 101 325 pascals. It began as the pressure of a 760 mm column of mercury at 0 °C under standard gravity, which is why the torr and the millimetre of mercury are still within a whisker of each other. The 10th CGPM fixed the modern value in 1954, deliberately choosing a round number of pascals rather than a round number of millimetres.

Being defined, it is exact and carries no uncertainty, unlike the actual atmospheric pressure at your location, which is a weather variable and averages nearer 101.0 kPa at sea level over a year. Use it as the reference for absolute pressure, for the standard boiling point of water, and for converting gauge readings: absolute = gauge + 101.325 kPa.

Used by 4 solvers

Gas Volume at STP

V=n VmV = n\,V_m

Gauge and Absolute Pressure

Pabs=Pgauge+PatmP_{abs} = P_{gauge} + P_{atm}

Hydrostatic Pressure (P = ρgh)

P=ρghP = \rho g h

Ideal Gas Law

PV=nRTP V = n R T
Revised 16 October 2026
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formula.expert. (2026, October 16). Standard atmosphere. https://formula.expert/constants/standard-atmosphere