International Standard Atmosphere (ISA)

The International Standard Atmosphere (ISA) has been agreed to by many representative countries and entities in the aviation field. It is a representative model of the atmosphere and not an average. Most of the participants in aviation are in the northern hemisphere so this standard is based on the range of local weather conditions that occur in their locations. The standard results will need to be adjusted to suit weather conditions elsewhere.



Metric unit

Imperial Unit

Pressure, P 101.3 kPa 2116.7 lbf/ft2
Density,ρ 1.225 Kg/m3 0.002378 slug/ft3
Temperature,T 15oC , 288.2 K 59 oF , 518oR
Speed of Sound, a 340.3 m/s 1116.4 ft/s
Viscosity,μ 1.789 x 10-5 Kg/m/s 3.737 x 10-7 slug/ft/s
Kinematic Viscosity, ν 1.460 x 10-5m2/s 1.5723 x 10-4ft2/s
Thermal Conductivity, k 0.02596 W/m/K 0.015 BTU/hr/ft/oR
Gas Constant, R 287.1 J/Kg/K 1715.7 ft lbf/slug/oR
Specific Heat, Cp 1005 J/Kg/K 6005 ft lbf/slug/oR
Specific Heat, Cv 717.98 J/Kg/K 4289 ft lbf/slug/oR
Ratio of Specific Heats, γ 1.40
Gravitational Acceleration, g 9.80665 m/s2 32.174 ft/s2