Method of estimating the volume (Vtk) of a tank (1), comprising: a step of calculating the volume (Vtk) of the tank (1) by applying the law of conservation of enthalpy (H) of the gas, considering that the transfer of the checking stream of gas is adiabatic (Ttk(t1)=Ttk(t2) and Tsi(t1)=Tsi(t2)), expressing the enthalpy of the gas in the tank as a function only of the temperature Ttk(ti) of the gas and the pressure Ptk(ti) of the gas (Htk=function of (Ttk(ti); Ptk(ti)), using the perfect gas law or a Van der Waals equation of state expressing the volume of the tank Vtk(ti) (in cubic meters) only as a function of the known or previously estimated variables.