This International Standard Atmosphere calculator is based on the U.S. Standard Atmosphere, 1976 document published by the NOAA, NASA and USAF.
Features
Absolute accuracy, including molecular scale temperature between 80 and 86 km.
Riemann sum approximation of integrals for pressure and density above 86000 m. No lookup tables!
Clickable altitude graphs.
Number Density of individual species graph.
Switch from linear to logarithmic scale for pressure and density curves.
Calculations
Strict adherence to the equations and constants is maintained throughout this calculator, with the exception of a few typographical corrections (e.g. number density for He is 7.5817x1014).
Some constants are alterable, or improved for accuracy based on updated empirical observations. The effect on output is minimal.
Calculations of pressure and density above 86000 m' are derived using a right Riemann sum to approximate the integrals in equations (35),(38),(39) and (40). dZ is set to 100 meters, but can be adjusted.
When entering density or pressure with a temperature offset, the resulting altitude is approximate. No calculation is made above 90000 m.