Thermographic devices that are able to acquire images, such as infrared line scanners (IRLSs), are becoming increasingly popular. One of the major issues when working with this kind of device is spatial calibration, which is necessary to extract metric information from images. In this paper, a spatial calibration procedure for IRLSs is proposed. The procedure is based on a geometrical model to calculate the spatial position of all of the samples. The model also calculates the length of the semiaxes of the elliptical surface of all of the samples. In addition, an uncertainty analysis has been carried out, providing the combined standard uncertainty of the measurement. This analysis provides information about the uncertainty of the spatial calibration procedure, which is a function of the standard uncertainty of the IRLS parameters. The spatial calibration procedure has been applied to a commercial IRLS to verify the proposed process. The result of the spatial calibration procedure is a straightforward method to calculate the position and dimensions of all of the temperature samples. This work is an important contribution to the development and exploitation of infrared image processing systems.