The proposed technique computes the roto-translation parameters of multiple mmWave radar devices respect to a reference coordinate system. The method calibrates radars in pairs and it is based on computing the optimal rigid transformation that matches the movement trajectories of multiple targets in the environment that are tracked by both radars. A dedicated association cost function has been designed that is able to identify the best track-to-track matches to perform calibration. The cost function is composed of terms that account for (i) the residual error of two tracks after application of roto-translation, (ii) the time synchronization between two tracks, (iii) the length of tracks. The technique is then able to automatically evaluate quality of the calibration by computing the residual matching error and re-calibrate if needed.