* Diameter of Mars: 6,779 kilometers (4,212 miles)

* Diameter of Phobos: 22.2 kilometers (13.8 miles)

* Diameter of Deimos: 12.6 kilometers (7.8 miles)

Combined Diameter:

6,779 km (Mars) + 22.2 km (Phobos) + 12.6 km (Deimos) = 6,813.8 kilometers

Therefore, the combined diameter of Mars and its moons is approximately 6,813.8 kilometers.