ISA Calculator
Enter one property to calculate the others based on the International Standard Atmosphere model. Note: Calculating from temperature is only valid in the Troposphere.
Interactive Standard Atmosphere
Hover over the chart to see ISA values at different altitudes.
About the ISA Model
The International Standard Atmosphere (ISA) is an idealized model representing average atmospheric conditions (temperature, pressure, density) at different altitudes. It provides a common reference for aviation, aerospace engineering, and meteorology.
Key features of the ISA model:
- Defines standard sea level conditions: Temperature 15°C (288.15 K), Pressure 1013.25 hPa (101325 Pa), Density 1.225 kg/m³.
- Divides the atmosphere into layers with defined temperature lapse rates (how temperature changes with altitude):
- Troposphere (0-11km): Temperature decreases linearly at 6.5°C/km from 15°C at sea level to -56.5°C at the tropopause.
- Tropopause (11-20km): Constant temperature layer at -56.5°C.
- Stratosphere I (20-32km): Temperature increases at 1.0°C/km.
- Stratosphere II (32-47km): Temperature increases at 2.8°C/km up to -2.5°C.
- Stratopause (47-51km): Constant temperature layer at -2.5°C.
- Mesosphere I (51-71km): Temperature decreases at 2.8°C/km.
- Mesosphere II (71-84.85km): Temperature decreases at 2.0°C/km to -86.2°C.
- Assumes dry air, constant chemical composition, and gravity that only varies with altitude.
- Provides equations to calculate properties at any given geometric altitude up to 86 km.
This calculator implements the ISA model equations to find atmospheric properties based on a given altitude, pressure, or temperature. Inversions (calculating altitude from pressure or temperature) may have limitations, especially in isothermal layers.