This paper aims to establish and develop a calibration model for two time-of-flight terrestrial laser scanners (TLS): Trimble GX200 and Riegl LMS-Z390i. In particular, the study focuses on measurement errors and systematic instrumental errors to compile an error model for TLS. An iterative and robust least squares procedure is developed to compute internal calibration parameters together with a TLS data set geo-reference in an external reference system. To this end, a calibration field is designed that performs as an experimental platform that tests the different laser scanner methods. The experimental results show the usefulness and potential of this approach, especially when high-precision measurements are requires.