Measuring the thickness of steel plates during the hot rolling process is crucial for getting the necessary feedback to obtain the desired values at room temperature.The dilatation and the phase transformations of steel occur during heating and subsequent cooling and rolling strongly influences the results of thickness measurements.The radiometric method provides the necessary means for making real-time and fully automatized measurements of steel thickness during rolling,if only the temperature correction is precisely known and taken into consideration.This article proves that the experimental results concerning the relative variation of steel thickness and corresponding mass-thickness variation can be correctly explained by means of the theory of metal dilatation correlated with the theory of nuclear radiation absorption when passing through a metal or metallic alloy,such as steel. Measuring the thickness of steel plates during the hot rolling process is crucial for getting the necessary feedback to obtain the desired values ​​at room temperature. Dilatation and the phase transformations of steel occur during heating and subsequent cooling and rolling strongly influences the results of thickness measurements The radiometric method provides the necessary means for making real-time and fully automatized measurements of steel thickness during rolling, if only the temperature correction is precisely known and taken into consideration. This article proves that the experimental results concerning the relative variation of steel thickness and corresponding mass-thickness variation can be correctly explained by means of the theory of metal dilatation correlated with the theory of nuclear radiation absorption when passing through a metal or metallic alloy, such as steel.