During 2002, 109 Felicitas was observed by radar from the Arecibo Observatory. The return signal matched an effective diameter of 89 ± 9 km. This is consistent with the asteroid dimensions computed through other means.
^ abcdPravec, P. et al. (May 2012), "Absolute Magnitudes of Asteroids and a Revision of Asteroid Albedo Estimates from WISE Thermal Observations", Asteroids, Comets, Meteors 2012, Proceedings of the conference held May 16–20, 2012 in Niigata, Japan (1667), Bibcode:2012LPICo1667.6089P.