 In the 1970s, radiometric observations were published in the Tucson Revised Index of Asteroid Data (TRIAD) compilation gave a diameter of 173.0 kilometers with a radiometric albedo 0.021.According to the space-based surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, "Diomedes" measures between 117.786 and 172.60 kilometers in diameter and its surface has an albedo between 0.028 and 0.061.The "Collaborative Asteroid Lightcurve Link" adopts the results obtained by IRAS, that is, an albedo of 0.0313 and a diameter of 164.31 kilometers based on an absolute magnitude of 8.30.