Density of Air

Derivation of a Reduced Equation for the Density of Air

Douglas Goncz

Replikon Research

PO Box 4394

Seven Corners, VA 22044-0394

April 2018


Starting from published equations and first principles for the density of humid air as a function of

partial pressure of dry air and of water vapor with equations for total pressure and a model for relative humidity,

a derivation is presented here, step by step, with justification for each step,

leading the reader to a final equation in condensed computationally efficient form for

the density of air in kilograms per cubic meter as a function of three observable variables only:

barometric pressure in Pascals,

relative humidity in percent relative humidity, and

temperature in degrees Celcius,

resolving physical constants to numerical constants

compatible with measurements of common accuracy and precision.

Then, a version of the final equation suitable for Copy and Paste into computer code is given.