Gas diffusion calculates the binary diffusion coefficient for a pair of gasses as a function of the temperature and the pressure. The app is simple to use yet highly accurate and accounts for the dipole moments as well as the interaction between polar and non-polar gasses. The method presented in “A fortran computer code package for the evaluation of gas-phase multicomponent transport properties” is used which have been extensively verified against state-of-the-art software and validated against experimental data to ensure the quality of the results. The binary diffusion coefficient can be determined in either the SI unit system or the Imperial (US) unit system.