A procedure is described to determine the thickness of a plate material by infrared scanning. It consists of heating the material with a moving heat source and measuring the temperature of the plate by infrared scanning when the material has reached a quasisteady state. At that time, the initial temperature has been damped out, and the plate temperature becomes invariant with time in the moving coordinates of the heat source. The plate thickness can thus be determined independent of the initial temperature of the plate, and the infrared image can be analyzed more conveniently for an accurate determination of the plate thickness. This paper covers the analysis and experiment for infrared scanning. The uncertainty in the measurement is found to be within one gauge size of the plate thickness tested. ©1995 American Institute of Physics.