A method and an apparatus for measuring the thickness of a metal layer. The metal layer has a resistivity (ρ1) that differs from the resistivity (ρ2) of the metal object. The apparatus includes a first device arranged to generate a magnetic field in close vicinity of the metal layer, and to generate a variation of the magnetic field so that a current is induced in the surface of the metal layer, a second device arranged to measure the changes of the magnetic field outside the metal layer due to the induced current during a time period that is longer than the time it takes for the current to propagate through the metal layer, and a computing unit to determine the thickness of the layer based on a mathematical relation between the thickness of the layer and the measured values of the changes of the magnetic field.