A method of measuring the thickness of a coating layer of a workpiece, the layer being formed on a substrate of the workpiece. The method comprises several steps. First, feeding a probe alternating electrical signal to induction device in order to induce a magnetic field in the workpiece. Second, measuring at least one physical characteristic that varies as a function of the magnetic field induced in the workpiece. Third, determining first and second values of an indicator, the values being determined respectively from measurements of the physical characteristic taken when the electrical signal has first and second given frequencies. Forth, calculating the difference between the first and second values of the indicator and determining the thickness of the coating layer as a function of the difference and of predetermined data correlating: the difference between the values of the indicator; and corresponding values for thicknesses of the coating layer.