Film thickness may be measured with a dial micrometer. A reading is first taken on the hard dry paint film, and then a small strip of the film (including the measured point) is carefully removed and another reading taken on the substrate the difference in readings representing the thickness of film removed. This method relies on fairly hard films and accurate removal of the film only.

Another method suitable for ordinary (non-magnetic) paints on iron and steel relies on a gauge having a strong permanent magnet at the base, which is placed in contact with the paint film. The magnetic flux across the air gap in the instrument will vary with the proximity of the steel or iron panel, and the coating on it acts as a magnetic air gap between the panel and the meter contacts.

The gauges are usually calibrated to give direct readings. Several varieties of electro-magnetically operated thickness gauges are available. They allow thicknesses to be measured without destroying or marring the coating. Where non-ferrous substrates like aluminium, copper or zinc instruments can be used which work on the principle of recording variations in induced eddy currents, their strength varying inversely with variations in thickness of the coating.