ISA Atmosphere Calculator
Calculate standard atmosphere properties at any altitude in the troposphere.
ISA Reference Values
| Property | Sea Level Value |
|---|---|
| Temperature | 15C / 59F |
| Pressure | 1013.25 hPa / 29.92 inHg |
| Density | 1.225 kg/m3 |
| Lapse Rate | -1.98C per 1000 ft |
| Tropopause | 36,089 ft / 11,000 m |
ISA Formulas
Temperature: T = 15 - (1.98 x altitude/1000) C
Pressure: P = P0 x (T/T0)^5.256
Density: rho = P / (R x T)
Understanding the International Standard Atmosphere
What is ISA?
The International Standard Atmosphere (ISA) is a theoretical model of Earth's atmosphere defined by ICAO. It provides a baseline for comparing atmospheric conditions and calculating aircraft performance.
Troposphere vs Stratosphere
In the troposphere (sea level to 36,089 ft), temperature decreases with altitude at approximately 2C per 1000 ft. Above the tropopause in the stratosphere, temperature remains constant at -56.5C.
Practical Applications
- Aircraft performance calculations
- Flight level assignments
- Engine performance charts
- True airspeed calculations