Deimos is .004 times the diameter of the Moon. [see page for the Moon]
Deimos is .563 times the diameter of Phobos (a satellite of Mars).
Deimos is .185 times the diameter of Belinda (a satellite of Uranus).
Deimos is .143 times the diameter of Pandora (a satellite of Saturn).
Deimos is 0.06 times the diameter of Amalthea (a satellite of Jupiter).
Deimos is .032 times the diameter of Mimas (a satellite of Saturn).
for another comparison.