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Calculate barometric pressure in the International Standard Atmosphere

Uses ISO/ICAO International Standard Atmosphere (ISA) model to calculate a reference barometric pressure for any elevation up to the stratopause at 20km asl. Note that both the ISA and US Standard Atmosphere, 1976 (USSA) utilize the ideal gas law and identical physical constants up to 20km, and therefore give identical values throughout the troposphere. However, original documentation of the USSA along with sample tables are freely available (see reference below) whereas documentation of the ISA is not. Enter geometric altitude.
1 mb = 1 hpa.

Altitude-to-pressure

Altitude [m]	(-5000 to 20063)
[ft]	(-6560 to 65823)

0 m --> 0.00 mb

Constants
Gravity at sea level	g₀	9.80665	m s^-2
Height of tropopause^†	H_tp	11	km
Height of stratopause^†	H_sp	20	km
Temperature lapse rate	L	-6.5	degrees K km^-1
Molecular weight of air	M₀	28.9644	kg kmol^-1
Barometric pressure at sea level	p₀	101325	Pa
Barometric pressure at tropopause	p_tp	22632	Pa
Universal gas constant	R^*	8.31432	J K^-1 mol^-1
Radius of earth	r₀	6356766	m
Temperature at sea level	T₀	288.15	degrees K
Temperature at tropopause	T_tp	216.65	degrees K

--
^†units of geopotential length

References

CRNS Lab, 2023, Standard Atmosphere. [online] Available at: https://crnslab.org/util/atmo.php [Accessed Day Month Year].

International Civil Aviation Organization (ICAO) Doc 7488/2 - ICAO Standard Atmosphere (Second Edition).

U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D. C., 1976. Download