Can I use any reference area for lift and drag coefficient? I know that for rockets they often use the circular cross-section S_reference for the drag prediction: drag = rho/2 v^2 * c_D * S_reference

For aircrafts they use the chord length of a wing as S_reference.

So when I want to compare those to for their aerodynamic performance, can I just use 
S_reference{rocket} * C_D{rocket}

and S_reference{aircraft} * c_D{aircraft}

So to my mind: I can always use any reference area I want for determining c_D , but when I want to compare two bodys for their aerodynamic performance, I have to use: c_D * S_reference 

Thanks for your opinion,
The reference area is chosen according to the flow profile:


For long slender bodies, the wetted area is chosen because the main drag source is the shear forces between the boundary layer and the free flow.
For relatively short bodies, the cross-sectional area is most relevant because of the much larger contribution of pressure differential between front and aft of the stream.


Directly comparing $C_D$ of rockets and aeroplanes would not be very useful, because the reference area for aeroplanes is the wing area, which rockets do not have. Indeed $C_D$ * A is a much more useful comparison, if one knows what reference area A was chosen.