In the standard atmosphere:
* T is  (= ), giving a theoretical value of  (=  =  =  = ). Values ranging from 331.3 to 331.6 m/s may be found in reference literature, however;
* T is  (=  = ), giving a value of  (=  =  =  = );
* T is  (=  = ), giving a value of  (=  =  =  = ).
In fact, assuming an ideal gas, the speed of sound c depends on temperature and composition only, not on the pressure or density (since these change in lockstep for a given temperature and cancel out). Air is almost an ideal gas. The temperature of the air varies with altitude, giving the following variations in the speed of sound using the standard atmosphere—actual conditions may vary.
Given normal atmospheric conditions, the temperature, and thus speed of sound, varies with altitude: