Abstract: Apparatus are provided for measuring coating thickness. The apparatus include first and second inductors, which may be coils, and measuring the impedance of conductors by passing alternating current through the conductors. The conductors are arranged so that the first inductor may be positioned sufficiently close to a conductive surface so that its impedance changes and, when so positioned, any change in the impedance of the second inductor brought about by the surface is negligible compared to that in the impedance of the first. A microprocessor is provided and arranged to calculate a temperature compensated thickness measurement from the measured impedances of both inductors.