# 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

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.