Yes, ahmed osama, you are absolutely right.
First, you measure the current through the primary, without any load in the secondary. Then you measure the DC resistance of the primary (with an ohmmeter). From that you calculate the actual primary inductance, or magnetizing inductance, as it is sometimes called.
Then you measure the secondary voltage, again without any load. Since the primary to secondary voltages are related by the relation Vp/Vs=Np/Ns, you can calculate the turns ratio of the transformer. You have to be careful, though, if you really want to be accurate. The voltage across the "primary" is actually the voltage across the L of the primary (remember, you have an R in series with it, though to a first approximation you can consider the entire mains voltage is across the L, neglecting the drop across the R).
(Np/Ns)≈Vp/Vs
Once you know the turns ratio you can easily calculate the secondary inductance, knowing that the ratio of the inductances is equal to the square of the turns ratio:
Lp/Ls=(Np/Ns)² so Ls=Lp(Ns/Np)²
Regards,
VVV