Theoretical Antenna Efficiency calculation formula using Gain comparison method

As I have the practical value table of AUT gain ,Ref antenna gain, AUT maximum received power ,Ref antenna maximum received power (dB) and cable losses value, I am bit unsure about the theoretical formula to calculate the efficiency using Gain comparison method.It would be highly appreciated if anyone could come forward to sort out my problem.Thanks

Are you trying to calculate antenna apature efficiency?

yes please