Calculating The Altitude Of A Known Pressure

Constants:
5.2558797 = Mg/RT', where M is the (average) molecular weight of air, g is the acceleration of gravity and R is the gas constant.

6.8755856 * 10^-6 = T'/T_0, where T' is the standard temperature lapse rate and T_0 is the standard sea-level temperature.

(See also Altitude = (10^(log(PF/PS)/5.2558797)-1)/-6.8755856*10^-6)