Mykul10
Mach No is a percentage value of the speed of sound ie 0.85 = 85% speed of sound. Unfortunately the speed of sound changes with pressure but at sea level is around 760 mph and decreases as pressure decreases.
Small correction
....sound. Unfortunately the speed of sound changes with (Abs) temperature but at sea level is around 760 mph and decreases as temperature decreases.
M (dry air within reasonable temperature limits) = Sq.Rt (Gamma x R* x Tabs)
R* is a combined gas molecular value
Gamma is 1.4 (truly adiabiatic compression wave)