Refractive Index of Air Calculator
Calculate the refractive index of air using the modified Edlén equation (Birch & Downs 1994) with humidity correction. Accounts for wavelength, temperature, pressure, humidity, and CO₂.
The refractive index of air deviates from unity by roughly 2.7 × 10⁻⁴ at standard conditions — small but significant in interferometry, laser ranging, and any path-length-sensitive measurement. This calculator applies the modified Edlén equation (Birch & Downs 1994) with Peck & Reeder dispersion to compute n(λ, T, P, RH, CO₂) at wavelengths from 300 to 1700 nm. Inputs are vacuum wavelength, air temperature (5–45 °C), total pressure (80–110 kPa), relative humidity (0–100 %), and CO₂ concentration. Outputs include the refractive index to eight decimal places, the shortened in-air wavelength, optical path length correction per meter of air path, and a breakdown of individual contributions from dispersion, CO₂ deviation, and humidity.