I beg to differ -
example FL330 ISA condition and IAS 480kts.
What would be the TAS?
Pht = 33,000 : CAS = 480 : TAS = 732.5 : Mach No. = 1.2592 : EAS = 423.6
I get the feeling from the basic nature of the question that the original poster is at the training stage, i.e. fairly slow aircraft and at or below 10,000 feet. If so just use the CAS and Density Height calculation available from any old 'garden variety' pilot computer to obtain TAS.
The resultant airspeed is actually more correctly referred to as Density Air Speed (DAS), but at Mach Numbers <0.5 and below 10,000 feet, the error is negligible.
If I'm wrong in assuming the status of the question poster, then there's much more to be said.